PIL is not a dependency of OpenWPM proper, so it would be inappropriate
to list it in requirements.txt, but it _is_ used by one of the tests.
Kludge a direct installation command into .travis.yml.

This should get us 90% of the way to Python 3 support.

This module was completely removed in Python 3.

This may mean install.sh now needs to install something called 'GeckoDriver',
but let's see if we can get away without it.

 * Rationalize import ordering in some files.
 * Don't run nontrivial code at module scope when invoked as __main__.
 * If jpm is not available, but the .xpi exists, don't bomb out.

Since Selenium 3.3 requires a 'geckodriver' executable in
the PATH, put <root_dir>/firefox-bin in the PATH if it exists,
and rely on PATH search to find 'firefox'.

 * Replace Adblock Plus with uBlock Origin
   (which does not need precached filter lists)
 * Replace Ghostery with Disconnect (ditto)
 * Update HTTPS Everywhere to latest version

We _might_ be down to just HTTP instrumentation problems at this point.

The behavior of `open(path, "a+")` differs between Python 2 and Python 3.
In the latter, it will try to seek to the end, and if this fails (e.g. if
`path` is a pipe) it will throw an exception.  To work around this we
have to monkey-patch selenium.webdriver.firefox.service.Service.

sqlite3 fetchall() has always returned an array of tuples even when
the query returns a single row; Python 2's sloppy cross-type comparisons
let us get away with it.

it doesn't exist

The commit also moves us from using `firefox_profile` to
`firefox_options` to set preferences. The Options interface has no
"frozen" or restricted preferences.

Selenium 3 + geckodriver don't (currently) self-identify in the DOM

OpenWPM requires a specific version. Instead, let's suggest the user
run the install script.

The multiprocess library used `dill` where multiprocessing would
normally use `pickle`. The main benefit is flexibility in the types of
arguments we can pass to `run_custom_function`.