Add version information to form list

[JacquelineMorrissette]

1. [N/A] If you've added code that should be tested, add tests
2. [N/A] If you've changed APIs, update (or create!) the documentation
3. Ensure the tests pass
4. Make sure that your code lints and that you've followed our coding style
5. Write a description of your work suitable for publishing on our forum
6. Mention any related issues in this repository (as #ISSUE) and in other repositories (as kobotoolbox/other#ISSUE)

Description

The <version> tag in the formList will now show the version information based on what was sent to KoBoCat from KPI at the time the form was created or updated. What is returned will depend on when the form was last updated. The possible items that can be returned include the UID, the version number and date, or it may return nothing.

To update this field:

• Login to KPI
• Go to the form you wish to display the version number and date
• Edit the form - Note: it is not required to change anything within the form
• Press save
• Redeploy the form

Related issues

Fixes #674
Related to kobotoolbox/kpi#3046

[noliveleger]

KoBoCAT in Python 2 is frozen. We won't make anymore change to this version. Let's do the work on KoBoCAT 2.0

[JacquelineMorrissette]

Reopening so it can be merged into master for the next release
No need to make any changes to the base branch since it is even with master

[jnm]

For reference, #685 is the KoBoCAT 2.0 PR