Fix indents and white space
Parse geometry in one place
Do screen geometry detection at one place

Idea from #51.
Fix incorrect use of XRRCrtcInfo width and height

The protocol reference says that these values are modified by the
rotation, projection matrix and Border property.
Applying rotation on them again will result in incorrect values.
Use XRRCrctInfo only when a correct output is set

The higher level method of getting the screen size from the current
screen configuration is taken with slight modifications from #51.