Migrated protected methods to private implementation

This commit migrates two protected functions in
ContentItemInterface that should not be provided in public
API: emitPropertyChangeSignals and initializationComplete.
Some cleanups

This commit includes some cleanup, like removing useless headers,
reordering includes (alphabetical order, first Qt includes etc.)
reordering members (first methods then attributes) and cleanup
in variable names. It also tries to trim lines in order for
them to be lesser than 100 characters.