cmd/compile: display Go code for a function in ssa.html

cmd/compile: display Go code for a function in ssa.html

This CL adds the "sources" column at the beginning of SSA table.
This column displays the source code for the function being passed
in the GOSSAFUNC env variable.

Also UI was extended so that clicking on particular line will
highlight all places this line is referenced.

JS code was cleaned and formatted.

This CL does not handle inlined functions. See issue 25904.

Change-Id: Ic7833a0b05e38795f4cf090f3dc82abf62d97026
Reviewed-on: https://go-review.googlesource.com/119035
Run-TryBot: Yury Smolsky <yury@smolsky.by>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>