Implemented the basis of the interface
+ Created a fragment from where the operation can be dragged
+ Created a fragment which contains the main screen
+ Created a drawer layout
+ Added resources (our color palette and some images needed for the drawer layout)
- Removed some unnecessary auto-generated code

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Started on the basis of the logic that draws (and measures) the formulas which are stored in MathObjects

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Integrated the engine with the interface class structure.
From now on we'll be using Symja for the mathematical calculations.

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Discovered that the application package was still set to com.example.math_dragon.
Changed it to the right one (org.teaminfty.math_dragon).

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Subtract methode plus een methode voor het checken van lege childs
vermenigvuldigen toegevoegd
The new operators (multiply and subtract) are now tested.
Also removed some unnecessary imports.

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
More convenient methods added to MathBinaryOperation and exception handling.
Merge https://github.com/Divendo/math-dragon

Assigning members to binary operations now is very awkward because you explictly need to specify the index number on each getter and setter. The next logical step is to derive MathOperationBinaryLinear from MathOperationBinary.