Fixes: #467

Fixes: #202

To send notifications, sendalerts calls Flip.send_alerts().
I updated Flip.send_alerts() to be a generator, and to yield
a (channel, error, send_time_in_seconds) triple per sent
notification.

coveralls.io is throwing 422 and breaking CI,
this may or may not help.

Related: https://github.com/TheKevJames/coveralls-python/issues/252

The initial implementation was just calling signal-cli directly
using `subprocess.run`.

Going with DBus makes it easier to shield signal-cli from the
rest of the system. It also makes sure the signal-cli daemon is
running in the background and receiving messages. This is important
when a recipient does the "Reset secure connection" from the app. We
must receive their new keys, otherwise our future messages will
appear as "bad encrypted message" for them.

With the previous 10 minutes / minute limit we were still hitting
Telegram API rate limit (the 429, "Too Many Requests" response)
from time to time.

Therefore, tighten the limit a bit on our side.

The PhoneNumberForm is used in "Add SMS" and "Add Phone Call" pages.
The PhoneUpDownForm is a subclass of PhoneNumberForm and
adds "up" and "down" boolean fields. It is used in "Add Signal"
and "Add WhatsApp" pages.

Fixes: #428

Fixes: #465

Need it to escape quirks mode in email clients.

Fixes: #347

Not using them anywhere on the site currently, so commented them out
in bootstrap.less and regenerated bootstrap.css.

Fix simple typo in docs, libary -> library

There is a small typo in templates/docs/python.md.

Should read `library` rather than `libary`.

Fixes: #348

Fixes: #462

Fixes: #450