Get rid of back-end localization (and remove it from Dockerfile)

[maxpatiiuk]

Back-end support for localization was added in 7.6
However, back-end infrastructure for localization is not compatible with the front-end solution.
Maintining two systems for localization is bad
Instead, back-end localization should be scrapped and front-end should be the sole place for all UI localization strings.
If back-end needs to print a localizable message, it should have predefined responses/enums that are then localized by the front-end

[maxpatiiuk]

This will allow to remove the following things from Dockerfile:

• Installing gettext
• This block:

# The following is needed to run manage.py compilemessages:
# The secret key file needs to exist so it can be imported.
# The INSTALLED_APPS needs to be cleared out so Django doesn't
# try to import the Specify datamodel which isn't defined yet.
RUN echo "SECRET_KEY = 'bogus'" > specifyweb/settings/secret_key.py
RUN echo "INSTALLED_APPS = ['specifyweb.frontend']" >> specifyweb/settings/__init__.py
RUN (cd specifyweb && ../ve/bin/python ../manage.py compilemessages)