packaging: add global installation support for linux

- avoid using fixed paths and find LRC either when globally installed or located in custom directory
- add installation rules for binaries, .desktop files, .appdata.xml, logo and doc
- add support for generating and copying runtime files (webresources and translations)
- add launcher script (client qt/gnome/kde selector)
- add uninstall support
- add missing sources (moderatorlistmodel)
- update README

Gitlab: #160, #230, #263, #264

Change-Id: I3fee77a917be038072a20c7f99b510f9a8bf65b4