Added two standard paths to file open/save dialog

In particular Desktop and Downloads have been added.
Also introduced a new function to create a file dialog
in order to prevent code duplication.
Loop marker: Changed tooltip text.
Update timeline.cpp
MainWindow: Moved FileDialog to own subclass
Update code to use FileInfo instead of QFileInfo

Also removed all blocks similar to
```
#if QT_VERSION >= 0x040806
	filedialog.setOption( QFileDialog::DontUseCustomDirectoryIcons );
#endif
```
as this now takes place in the new subclass's constructor.
Add new class VersionedSaveDialog

A file save dialog (inherits FileDialog) that provides buttons to
increment or decrement a version which is appended to the file name.
(e.g. "MyProject-01.mmpz")
Add "Save as new version" action to project menu

Use Shortcut Ctrl+Alt+S. Part of issue #86
Make LFO controller accept custom waveforms
Tooltip: Changed tooltip text of LFOControllDialog of custom waveform
Travis: Set build mode to RelWithDebInfo

This may lead to build errors, as variables that are only used in asserts
will get optimized out and because of -Werror being set (unused variables).
Fix some warnings
Plugin browser: Sort plugins by display name
Added unfa-Static.mmpz to /data/projects/CoolSongs and updatet LICENSES.txt file there.
Merge pull request #136 from unfa/stable-0.4

Added unfa-Static.mmpz to /data/projects/CoolSongs and updatet LICENSES....
Merge pull request #135 from Lukas-W/stable-0.4-iss106

Plugin browser: Sort plugins by display name
Merge pull request #134 from Lukas-W/stable-0.4-travis

Set build type to RelWithDebInfo
Merge pull request #132 from Lukas-W/stable-0.4

Update about window
Controllers Naming: Prevent duplicate names

For this, iterate through all given names and use the next name that's available.
Merge pull request #125 from wongcc966422/timelineDoc

Loop marker: Changed tooltip text.
Merge pull request #127 from wongcc966422/LFOBitinvaderVibedCustomWaveforms

Make LFO controller, Bit Invader and Vibed accept custom waveforms