Simplify the webapi test function names.

This removes all the redundancy in the test function names, in order to
shorten them. The type of resource has been removed from the names. So,
instead of test_get_file_attachment_with_foo, it's just
test_get_with_foo.
Add action hooks for the base page header.

The header contains the Review Board branding, as well as the find
input, account and support links. This change adds a
HeaderActionHook and HeaderDropdownActionHook that allows an extension
to add items to the header.

Reviewed at https://reviews.reviewboard.org/r/4624/.
Use the correct executable in setup.py

In setup.py, sys.executable contains the path of the current python interpreter
and one should use it when running a different script.

Testing done: On a system where the executable is /usr/bin/python2.
Reviewed at https://reviews.reviewboard.org/r/4633/