[ticket/11994] Make extension manager UI less misleading

Enable and Install were split into two different expressions.
Purge was renamed to uninstall to make clearer what is going to happen.

PHPBB3-11994
[ticket/11994] More language fixes

PHPBB3-11994
[ticket/11994] Fix functional extension tests

PHPBB3-11994
[ticket/11994] Replace spaces with tabs

PHPBB3-11994
[ticket/11994] Fix some language

PHPBB3-11994
[ticket/11994] Use display name on confirmation screen

PHPBB3-11994
[ticket/11994] Update functional tests with display name

PHPBB3-11994
[ticket/11994] Make install/enable just one UI thing

PHPBB3-11994
[ticket/11994] Rename "uninstall" to "delete data"

PHPBB3-11994
[ticket/11994] Fix tests after uninstall rename

PHPBB3-11994
[ticket/11994] Fix more language

PHPBB3-11994
[ticket/11994] Change error level for missing .json file

PHPBB3-11994
[ticket/11994] Filter crawler for better search comparisons

PHPBB3-11994
[ticket/11994] "Delete data" is only available for disabled extensions

PHPBB3-11994
[ticket/11994] Fix functional tests

PHPBB3-11994
Merge pull request #1845 from nickvergessen/ticket/11994

[ticket/11994] Make extension manager UI less misleading
Merge branch 'develop' of https://github.com/phpbb/phpbb into ticket/12005