Change directory layout for QML code and plugins
Create libPresquileCore library and solve some CMake problems
Set project version in CMake
Use INSTALL_TARGETS_DEFAULT_ARGS
Stronger header include guards in core
Rename CoreUtils to PQStandardDirs
Remove QML 'internals' folder, which has been replaced by 'skeleton'
Compile with -DQT_NO_CAST_TO_ASCII -DQT_NO_CAST_FROM_ASCII -DQT_NO_KEYWORDS
Fix PQBaseItem coding style
Hardcode indentation step when generating QML

There's no need to have this customizable.
Optimize serialization of slides by passing around the original QTextStream

The serialized content is now written directly into the file via the stream
instead of being copied around within strings.
Move presentation and slide serialization to PQSerializer

Object serializeation is still handled by PQBaseItem, but having this in distinct
class allows for easier unit-testing later on and will be kept together with parsing
code.