docs: Fix a few typos

[timgates42]

There are small typos in:

• docs/configuration.rst
• docs/heroku.rst
• docs/wooey_ui.rst
• wooey/views/favorite.py

Fixes:

• Should read middleware rather than middelware.
• Should read existence rather than existance.
• Should read bootstrap rather than boostraped.
• Should read accessible rather than accssible.

Semi-automated pull request generated by https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md

[Chris7]

Handled in https://github.com/wooey/Wooey/pull/352 since one typo is not actually a typo