merge MathVariable and MathConstant to MathSymbol
Refactored MathSymbol. works a lot simpler now

Supports variables now as well.
Fixed comparison
fixen dat bij factor 1 de factor niet getekend wordt
nu echt gefixt.. ging wat mis
added the brackets to the bounding box of the derivative function

Signed-off-by: bvanr <henkibrij@hotmail.com>
Merge remote-tracking branch 'arian/symbol-constant' into work

Conflicts:
	src/org/teaminfty/math_dragon/view/fragments/FragmentMainScreen.java
	src/org/teaminfty/math_dragon/view/math/MathConstant.java
	src/org/teaminfty/math_dragon/view/math/MathVariable.java

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
MathSymbolEditor now supports the variables in the new MathSymbol
* Also made the names in the code consistent with the new symbol name (instead of "constant")

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