testing/kopano-webapp: seperate APKBUILDs per plugin

This removes all plugins that are available from other sources from this package and splits them into their own packages, thus fixing the issue with the different version numbers.

There's an awful lot of code duplication going on between the packages.

The usage of a -src package for kopano-webapp is mandatory because it's not (within reason) possible to ...

1. find the kopano-webapp version number at the time the sources array is put together
2. maintain a fixed version number for kopano-webapp in each kopano-webapp dependent package

Thus depending on kopano-webapp-src at build time is the only reasonable way to ensure that the kopano-webapp version in aports at build time is also used at build-time of the specific packages.

kopano-webapp-mdm depends on z-push (!23411 (merged))