[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.

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[ticket/11994] More language fixes

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

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[ticket/11994] Replace spaces with tabs

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[ticket/11994] Fix some language

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[ticket/11994] Use display name on confirmation screen

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[ticket/11994] Update functional tests with display name

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

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

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[ticket/11994] Fix tests after uninstall rename

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[ticket/11994] Fix more language

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

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[ticket/11994] Filter crawler for better search comparisons

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

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[ticket/11994] Fix functional tests

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

[ticket/11994] Make extension manager UI less misleading