Previously, web interface was assuming that the ith node in
the dot graph was being assigned the id "node<i+1>".  However,
this assumption was invalid when extra nodes were inserted
into the dot output (e.g., nodelets added for allocation
profiles).  Because of this bug, node selection by clicking
in the webui graph output would sometimes pick a random
string to match against.

The problem is now fixed by manually assigning an id to
every node in the generated dot graph.  dot will propagate
this id reliably to the svg output.

Updated the golden tests to reflect the new dot output.

Extended dotgraph_test.go with an -update flag that can be
used to update golden files.  Also removed a bunch of code
duplication in the test.

* Added info on focus/ignore/show/hide to legend on graphs

* Made separate function for formatting filters in legend

Previously we were showing filenames together with function names
when generating reports at function granularity. This was an attempt
to provide more information to the user, but it clutters the output.
Also, in cases where a function is associated to multiple files
(eg template instantiations in C++), keeping the filename may prevent
us from combining nodes from the same function.

Will stop keeping filenames at the default function granularity, and will
remove the "functionnameonly" option which was previously providing this
functionality.

By default hide entries in the comment field that starts with #, and
add a "comments" command to show all comments.

When reconciling samples, cleanup file paths to allow functions to be
combined if their source filenames match after cleanup (eg "src.cpp" and
"./src.cpp").

Also clean up existing uses of filepath to avoid passing empty strings
to it: filepath.Base("") returns "."

Also update the build instructions to use go get