This PR addresses some suggestions from a review, the most
important ones being:
	- Extracting the note split action to a separate method, called
Pattern::splitNotes
	- Removing getMouseTickPos method
	- Adding a variable that holds the current razor position and a
method to update it (quantizing if CTRL is not pressed)
	- Using [this] to capture "this" on the lambda function instead
of [=], since the latter doesn't work as intended from C++20 forward
	- Fixing some code style and adding comments

	By removing "&& noteUnderMouse()" from the mousePressEvent
conditional, we avoid an extra call to noteUnderMouse. The only
difference in the behavior of the tool is that now clicking on a place
that doesn't have a note will exit Razor mode.