fix range + message updates; implement album filter

[jgibbon]

• fixes some irregularities with updated/deleted messages chatmodel. messageIndexMap got out of sync for messages after deleted ones.
• adds media album
• reworks detail view for media messagecontents

this was mostly reworked/rebased in the middle of the night at 37C3, so it really needs some testing and a bit more clean up… I think I'll get to do some additional commits here. The main changes should be set, though.

Perhaps we give our "advanced users" a go with the usual disclaimer?

here are some rpms (zipped because of github restrictions): harbour-fernschreiber-0.17-12.aarch64.zip harbour-fernschreiber-0.17-12.armv7hl.zip harbour-fernschreiber-0.17-12.i486.zip

edit: this does not change anything in regards to the "reaction bubble" – perhaps a click on the date could also trigger the "general click"?