Bug #175: Completed quoting for parameters of some CMake commands

A Wiki article pointed out that whitespace will only be preserved for parameters
in CMake commands if passed strings will be appropriately quoted or escaped.
http://cmake.org/Wiki/CMake/Language_Syntax#CMake_splits_arguments_unless_you_use_quotation_marks_or_escapes.

Quoting was added so that more places should also handle file names correctly
which contain space characters eventually.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Merge pull request #285 from diizy/stable-0.4

AFP artwork, Zyn artwork update
AutomationEditor: fixed calculation of Y-coordinates for grid and values.
Merge pull request #288 from softrabbit/stable-0.4

AutomationEditor: fixed calculation of Y-coordinates for grid and values...
Merge pull request #231 from elfring/Complete_quoting_for_parameters_of_some_CMake_commands

Complete quoting for parameters of some CMake commands.
Update song_editor.cpp

A better way to update the play button icons, which requires less "if" checks and method calls in total.
Update piano_roll.cpp

A better way to update the play button icons, which requires less "if" checks and method calls in total.
Update AutomationEditor.cpp

A better way to update the play button icons, which requires less "if" checks and method calls in total.
Update song_editor.h

A better way to update the play button icons, which requires less "if" checks and method calls in total.
Update piano_roll.h

A better way to update the play button icons, which requires less "if" checks and method calls in total.
Update bb_editor.h

A better way to update the play button icons, which requires less "if" checks and method calls in total.
Update engine.cpp

A better way to update the play button icons, which requires less "if" checks and method calls in total.
Update bb_editor.cpp
Update AutomationEditor.h
Travis: added libfreetype6-dev as build dependency

We need libfreetype6-dev for building ZynAddSubFX/FLTK.
Merge pull request #290 from M374LX/stable-0.4

Better way to update play button icons
Revert ab44ef221e

libfreetype6-dev is not necessary, it is already part of other dependencies.
Add verbose make output to Travis CI
Fix a CMake quote sign problem

Caused by 95b0a4305ef8334bd4404983ab2195ce0e335f34
Merge pull request #294 from Lukas-W/stable-0.4

Fix wrong quoting in CMake