Fixes to undo/redo

Actually implemented in paste and cut. No more for loops, single-entry
references to the handsontable api.
blag
Copy/Paste/Cut should now work as designed.
Working on functions
=SUM now works from edit line
AVG SUM functions implemented. Synched input box and cells. Refined enter key presses.
Trying to implement funcTracker
Integrating function array
Fixed several bugs.  Function strings should now store properly, no matter how a cell is updated.
Fixed old average/sum button methods to be consistent with current sum/average function strings.
m
Synching text box

Works for simple typing. Need to work on getting caret position for
deletion/insertion.
Synching input box and cell input should now work in all known cases.
#ERROR now display when a function is syntactically incorrect
Simple cases should work
SUM and AVG in mathematical expressions, trying to fix parenthesis
stuff
Functions almost completely implemented

Some glaringly obvious issues- for example, cells not updating when
format changes. Ready for extensive testing soon.
format strings
Beginning implementation of relative cell references

Turn debug on in cellFunctions.js to activate. =A1 works, =$A1, A$1, and
$A$1 do not yet. Only works for single cell copying currently.