Attempted to add multiply button

Some logic errors. Due to a half hearted attempt at allowing long
calculations, such as 1+2+3. trying -1*2 or 2*-3 will both give the
wrong answer. Need to either remove features or make the feature
actually work.
Added list history, fixed negative numbers.

Added a class containing a BigDecimal and operatorFlag and made a list
of them to help make a history of calculations and to fix a problem with
multiplications involving negative numbers. Added a boolean that also
helps with the negative multiplications. Changed the way enumerators
worked, because my switch statement was flawed.
Code tidy up

Removed variable number1 which is no longer used. Rearranged declaration
of variables and added comments. Change addToHistory to addNumToHistory
and change the arguments so that this method automatically sets the
operatorFlag to none, change every instance of addToHistory. Will
eventually need method addOpToHistory for the operators. Delete
arguments that aren't necessary due to using public variables. Rearrange
methods in BIDMAS order for convenience. Slightly alter switch
statement, move reset() method from the end of each case to outside he
statement.