Add progress bar to ahat.

It can take a while for ahat to process a heap dump. This change adds an
ascii progress bar to ahat as it processes a heap dump.

Other changes worth noting:
* Adds progress tracking functionality to the dominators computation.
* Updates Parser to use builder pattern to make it easier to specify
  different parsing options.
* Stops pretending ahat runs with Java 1.7.

Sample output:

Preparing localhost/127.0.0.1:7100 ...
Processing 'foo.hprof' ...
[ 100% ] Reading hprof ...
[ 100% ] Resolving references ...
[ 100% ] Reversing references ...
[ 100% ] Initializing dominators ...
[ 100% ] Resolving dominators ...
Server started on localhost:7100

Bug: 68842538
Bug: 110129502
Test: m ahat-test
Test: Run on large heap dumps, manually inspect progress bar output.
Change-Id: I4903fef57371fa226f7802c50902319cb7506e68