On scroll trigger cMonScroll function

Contains mouseDown=false and also function to match scroll position on
both panes
Reworked render line and diff functions

renderLineStyle is now an array of style arrays
cMonScroll function added to move scroll position of other pane to match
The on('renderLine') event now covers all lines, a change since earlier
versions of CodeMirror
This means a reworking of code was needed here to firstly identify a
matching pane and then if we have a match, add the style. Done in a for
loop and considers array items in renderLineStyle
Reworked much of the updateDiffs functin to reset array & value to begin
with and push to renderLineStyle array now. Also only doing this if we
have a height higher than normal to set, for perf reasons
No need to set renderLineStyle to false anymore
Finally, sorted the order things happen into 2 logical sections - main
pane changes first then diff pane changes after