Fix some bugs and add message info page

Add MessageInfoPage.qml with small changes to models, and a bucketful of quality-of-life improvements!

• Remove obsolete, empty groups directory (fixes #296 (closed))
• Show a lock icon for GroupV2 groups, hide it for GroupV1 groups (fixes #317 (closed))
• Show only group size as group detail text
  • The header would only show a few phone numbers without wrapping anyway
  • The contacts can now be viewed with names and avatars in GroupProfilePage.qml anyway!
• Show self as first group member (picked from comments)
• Hide conversation page header in landscape orientation (fixes #314 (closed))
• Don't define height with all anchors defined
• Remove some QML debug output
• Don't wrap message sender name (fixes #332 (closed))
• Remove redundant QAbstractListModel casts (fixes #59 (closed))
• Fix quiet notification sounds again (this was broken in !293 (merged))
• Update main translation file
• Use warning icon and description only for GroupV1
• Display reactions using colored emoji → redesign emoji/info row

Edit: I rebased and rewrote the commits, so the texts above don't correlate to separate commits any more.

As I managed to intermangle add-message-info-page with this branch (sorry about that), also these:

• Get reactions with names from database and show them in MessageInfoPage
• Create MessageInfoPage.qml with basic set of information (fixes #428 (closed))

Some things to consider:

• Update readme for working Rust-in-sfdk instructions New issue
• Warn about old and insecure GroupV1
• Finalize reaction emoji layout (does the trick, let's polish it later)
• Is the QML method of getting the message model data acceptable?
• Fix message multi-selection QML logic to work with this
• Add stuff for message details
• Reactions are exposed without sender information (Recipient info is now fetched)
• Test on SFOS 3.4 (Jolla Phone)