Resolves #103 Custom header mechanism

[lbleier-GSFC]

Describe the contribution
Fixes #103, implemented the ability to allow users to select the header version byte offset, or custom offsets. In order to support this, some relatively major changes had to be implemented:

• A Python-native "mini" cmdUtil to send UDP data. The GroundSystem app in its current form is no longer dependent on the external C cmdUtil app (also fixes cFS ground system GUI Python code should generate cmd UDP directly #61, at least partially)
• Using Python's mmap module to share data between processes

Testing performed
Steps taken to test the contribution:

1. Make changes to code
2. Run program to verify functionality

Expected behavior changes
The update allows users to change the byte offsets for sending commands and parsing telemetry, to support different header versions or other implementations of cFS

Additional context

• Note that the "mini" cmdUtil is only a subset of cmdUtil's full functionality. Should the GroundSystem app be updated in the future, the full cmdUtil might need to be used again, or the "mini" cmdUtil updated accordingly
• There is a larger issue regarding the GroundSystem app as a whole and interprocess communication (IPC). There are multiple techniques to achieve this, but which technique is preferred, and whether or not GroundSystem should be completely redesigned to avoid IPC in the first place, is a discussion for the CCB.

Contributor Info - All information REQUIRED for consideration of pull request
Leor Bleier, NASA GSFC\Code 582

[skliper]

This PR has commits that are already in master. Can it be cleaned up such that we can review the actual change being proposed here?

[lgtm-com]

This pull request introduces 2 alerts when merging 1a3b6dc into 63b672a - view on LGTM.com

new alerts:

• 2 for Unused import

[lgtm-com]

This pull request introduces 2 alerts when merging 20fce30 into 63b672a - view on LGTM.com

new alerts:

• 2 for Unused import

[lgtm-com]

This pull request introduces 2 alerts when merging 449511e into 63b672a - view on LGTM.com

new alerts:

• 2 for Unused import

[lgtm-com]

This pull request introduces 2 alerts when merging e37501f into 63b672a - view on LGTM.com

new alerts:

• 2 for Unused import

[astrogeco]

This PR has commits that are already in master. Can it be cleaned up such that we can review the actual change being proposed here?

I think it's addressed now. Which commits did you notice were "duplicates"?

[lgtm-com]

This pull request introduces 2 alerts when merging e37501f into defa816 - view on LGTM.com

new alerts:

• 2 for Unused import

[lbleier-GSFC]

I did do some cleanup, but found a few last-minute issues that I pushed. I can squash those further if necessary

[astrogeco]

CCB 2020-07-01: APPROVED

Replace "enhancement" with a valid linking word: Linking a pull request to an issue

Open issue for cross-platform tmp location.

Open issue for ZMQ idea

[astrogeco]

@lbleier-GSFC if you still have time, can you take a look at the conflicts? If not, maybe @dmknutsen or @JandlynBentley-at-NASA can try

[lgtm-com]

This pull request introduces 2 alerts when merging fb58248 into aa15da9 - view on LGTM.com

new alerts:

• 2 for Unused import

[lbleier-GSFC]

@lbleier-GSFC if you still have time, can you take a look at the conflicts? If not, maybe @dmknutsen or @JandlynBentley-at-NASA can try

Should be good now