Fixed Mumble not remembering hidden dockwidgets

- Switch to custom mode if anything gets hidden/shown so
  auto-layouting code doesn't just unhide them on startup.
Abort drop when drag setting is invalid
Reduce probability for possible race until a real fix can be implemented

- p's target might be invalidated in the time between retrieving it and using it. https://mumble.hive.no/crashes/win32/1.2.4-145-g442b46e/2013-09-13T23:16%201.2.5%201.2.4-145-g442b46e%20Unknown.html seems to indicates that this happened at least once in Line 809 of AudioInput.cpp (mind the inlines).
- Should be fixed properly by using smart-pointers or removing this data interdependence between threads
Remove channel filtering from tray
Disconnect if for some reason we established a connection to a server without it having a certificate
First set of fixes for filter patch

Compare to review comments on https://github.com/mumble-voip/mumble/commit/304bf438daecad36285b8647b9bc72b685cf31ca

- No longer use channel name for identifying filtered channels.
  Switched to using server certificate digest combined with Channel
  id which works between servers and with duplicate channel names.
  The digest should be replaced by proper server identification soon.
  Ideally the client should keep a list which identifies servers
  by their address or - if a strong certificate is available - by
  certificate email. This can be re-used for tokens and other server
  dependent configuration.
- Changed naming from 'hidden' to 'filtered'
- Removed tray menu entry
- Removed global shortcut for channel hiding/showing
Fix channel flag handling with filter patch

- Channel comment flags were no longer clickable because
  filters weren't considered in offset calculation.
- What's this text didn't contain the flag icon
- Lowercased Flag.svg
- Magic numbers and abbreviation refactoring
- Lowercased Filter.svg and improved license display
update mumble_pt_BR.ts
Fixed leaving channel message not being sent when leaving the server
Add Ctrl+F shortcut for quickly enabling/disabling channel filtering
Default enable hide empty channel behavior for filter

- This should enable a discoverable first-time user experience
  with the filter and be usable without specifically selecting
  channels to filter. Using it in combination with the shortcut
  is quite handy even on small severs with many empty channels.
Expand "What's this" and tooltip for filter action
Make sure filter never hides the channel the user resides in.

- This only fixes the bug and doesn't perform the needed
  refactoring in the implementation of the channel filtering
  logic.
Update Opus to v1.1 beta release
Remove event handler for retired global channel filter shortcut
Re-implement UserEdit using Model/View paradigm to resolve various problems
with the old implementation.

- Added UserListModel.h/cpp as the backend for protobuf UserList editing
- Added UserListFilterProxyModel for filtering and sorting
- Re-implemented previous functionality in new environment
- This commit uses the new mumble coding style as found in http://mumble.sourceforge.net/New_code_guidelines
Fix application shortcuts not working in minimal mode.

Hiding elements of the UI like the icon toolbar disabled the
actions in it. As we want the shortcuts of the actions always
available we need to work around this behavior.

This patch adds all actions found in the object tree of the main-window
directly to the main window. As we don't use the auto-generated
context menu for that there shouldn't be any side-effects.

Another possible way would be to manually create QShortcuts and use
those instead. This would have much bigger code impact though.
Make userlist filter case-insensitive
Show channelid to ACLEditor
Update slice path for Ice 3.5.1