Consistency tweaks

Genrally, in MediaWiki, if things are not proper names, they are written without capitalisation, and sentence case is used, with only a capital at the start of a sentence.

Suggested by Siebrand:
https://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Revcs-hidehistory-present-supplement/en
https://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Revcs-error-edit-denied/en
https://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Revcs-edit-written/en
https://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Revcs-edit-preview-supplement/en
https://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Revcs-edit-preview-reason/en
https://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Revcs-alert-norevision/en_(6)
https://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Revcs-alert-nohistory/en
https://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Revcs-desc/en

Change-Id: I1e485fc5cf3d4fa857df51b8d027a95da5cffb5d
Merge "Consistency tweaks"