Implement a automod system for the Android custom app version_name

[kelson42]

gen-custom-android-build.py is the script used to create custom apps, ie. apps which include a unique content (ZIM file) and are rebranded.

If version_name is empty, then script gen-custom-android-build.py should try to take it from the ZIM file content. It can do that because:

• Custom apps versions are the date of the content, for example 2016-12
• This date is in the file name of the ZIM content.

So if there is not version_name, then gen-custom-android-build.py should try to extract the date from the ZIM file name which ends with it: for example "wikipedia_en_medicine_2016-12.zim" will give "2016-12".

[kelson42]

@EladKeyshawn If you could look at this one this would be great also. We are almost over to allow "automatically" to create new custom apps.

[kelson42]

This issue was moved to kiwix/kiwix-android#32