Created icons for the buttons

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Implemented scaling

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Merge branch 'master' into work

Conflicts:
	res/layout/fragment_main_screen.xml
	res/values/dimens.xml
	res/values/strings.xml
	src/org/teaminfty/math_dragon/MainActivity.java