[rpm/meecast.spec] Overhaul spec file, 2nd round

[Olf0]

Basically no altered functionality, but quite some changes in the spec file and another change in store:

1. Enhance the metadata for SailfishOS:Chum of MeeCast proper and added SailfishOS:Chum-metadata for all sub-packages.

2. Alter all version strings to adhere to Semantic Versioning ("SemVer"): three fields of digits (and an additional release string, as always), i.e. a.b.c-x.

3. Re-order the sub-packages, to let the event sub-package become the last one specified, in order to reduce confusion when reading the spec file, because of …

4. Split the Eventsview sub-package into two:

   • A sub-package eventview (a new name) for SailfishOS ≥ 4.6.0
   • A sub-package event (the original name) for SailfishOS < 4.6.0

   This allows to compile both sub-packages in one go and (more importantly) allows them to reside in the same repository (e.g. https://sailfish.openrepos.net/vasvlad/personal/main).

[Olf0]

@vasvlad, this PR is ready for review.

You can merge this PR if you think it is O.K., but there is another change I believe to be inevitable:
Please also take a look at PR Olf0#2 and tell me if you are fine with it. I am not happy about working around the flaws of the SailfishOS-OBS, but because the SailfishOS:Chum repository relies on it, I see no other way. If you have other ideas how to handle that, please let me know.

Thanks & cheers!