OSX editor fix, Wavetable library, imported sounds check

The main feature of this release the new local wavetable library. Until now, only wavetable editor window could be opened at once, and the only way to edit a previously created wavetable was to open it, provided that it was exported to sysex.
With this release, multiple editor windows can be opened, and there is a library window collecting all (previously and currently) saved wavetables. The wavetable library window is accessible from the "Windows" menu in every Wavetable editor window, from which you can access to all currently opened wavetable windows.
The wavetables are actually stored in SysEx .SYX format, within the user's data application folder. Wavetables can be imported, deleted or duplicated from the library window, and drag'n'drop works transparently within editor windows, for both imported file waves and single waves from the wavetable contents. This is a pretty new (and slightly complex) feature, and can be prone to bugs, crashes or unexpected behavior; I tested as much as I could, but, just in case, be sure to save your modifications often.

This release also partly fixes visualization problems for the Sound editor window under OSX. The interface is still not perfect (fonts are very small and there is a lot of unused space in the interface).

The MIDI/SysEx sounds and sound sets import now checks for invalid parameter values and asks the user for confirmation; invalid data can be left as they are (at your own risk), edited one by one, or globally fixed to minimum or maximum allowed values.

Other fixes:

• QtMultimedia requirement for Linux is now optional (due to some distributions not including it)
• Single sound dump from MIDI/SysEx sounds and sound set import dialog now works as expected
• Better handling of connection and selected items in the forementioned import dialog.
• Better detection of MIDI/USB connected Blofeld
• Fixes for wavetable drag'n'drop waves
• Handling of sound names improvements
• File import from the Library automatically detects the file type and acts accordingly, including wavetables (which are opened in the editor but not automatically saved in the library)

Known bugs:

• The degree character (°) cannot be used in Wavetable names, since it causes Bigglesworth to crash.
• It seems that in some OSX Sierra localization there can be an issue regarding unicode characters, which might cause Bigglesworth to not start up at all.
• OSX still suffers some visualization issues in the Sound editor window: fonts and widgets might look very small, and the Arpeggiator pattern editor tries to use much more space than needed, causing a vertical scrollbar to be shown.
• Sound editor window is still too big on OSX and Windows.
• Windows installer does not detect previously installed versions anymore.
• The wave visualization for imported files in the wavetable editor hides if the window is minimized.