Make refresh recompute the space the gutter takes up

When line numbers are off, and the editor was initialized in
a hidden position, the gutters would sit on top of the text.

Issue #2365
[overlay addon] Fix bug when overlay mode is itself multiplexed

It assumed it saw all parts of the stream, and started
doing bad things when that was not the case.

Issue #2410
Allow blankLine to return line-* and line-background-* strings

(Experimental for now. Prompted by indentation guide discussion.)
[real-world uses] Add Filemanager
Drop font-family rules from themes

Closes #2415
[haxe mode] Add 'abstract' keyword
Round top/bottom coords when drawing selection

To prevent gaps when browsers interpret fractional numbers oddly.
Use more meaningful names for drawSelection* functions
[closebracket addon] Fix: Trigger auto-close-triple behaviour after exactly 3 quotes.

Issue #2385
Better looking SVG badges in README.md.
[xml-hint addon] Support attributes that apply to all tags
Support electricInput as well as electricChars on mode objects

Issue #2412
[xml-hint addon] Filter out !attrs from top level completions
Work around Webkit bug where sometimes the sizer gets the wrong width

(It'll leave space for a scrollbar to the right of the sizer, though the
scroller does not actually have a scrollbar.)

Issue #2420
Set forceUpdate flag in refresh method

Closes #2431
[verilog mode] Rewrite
merged in changes