Centering text optional

The user can specify whether the text should be centered or stretched
over the available space
Merge branch 'feature-rectangular-showcase'

Conflicts:
	library/src/com/espian/showcaseview/ShowcaseView.java
Rewritten calculateTextPosition and draw in TextDrawerImpl to be more
flexible
Center title and text in available space
Added padding for the actionbar at the top of the screen and made text
width wider
Centering text optional

The user can specify whether the text should be centered or stretched
over the available space
Workaround for text going off screen without showcase view
Merge branch 'feature-better-text-positioning'

Conflicts:
	library/src/com/espian/showcaseview/ShowcaseView.java
	library/src/com/espian/showcaseview/drawing/TextDrawerImpl.java