[Feature Request] Use SAGA provided description and decorator files

[esnyder-rve]

There seems to be a number of SAGA tools which will not work with this plugin due to incorrect command calling (see also #21).

SAGA appears to ship with a zip file called "saga4qgis" which instructs the user to replace the plugin's description folder and processing/SagaNameDecorator.py file with the ones provided by SAGA.

Could this be automated within the SAGA NG Plugin? Having the user go through these steps seems a bit much for a plugin (especially when a plugin update overrides these files, and the user is confused on why things are broken again). This would cause the user to have to manually go through this process every time they either update this plugin, and change SAGA versions.

Possible Flow:

1. Trigger: Plugin Install/Update or SAGA version changed
2. Grab the saga4qgis.zip file located in the root of the provided SAGA folder
3. Extract the contents and place in their corresponding locations