Revert "[mms] Set infinite lifetime for the cache metadata for the Horde_Cache caching backend."

This reverts commit d5ceb8b2fc3f7538ae478b1192d6dccecd88b586.

Metadata is always touched when updating a message, so it will never
expire as long as the cache is being used.
For same reasons as Horde_Cache driver, it is ok to put a lifetime on metadata
ws
Button on bottom to match other prefs screens
Make these advanced preferences
Better text for this button

This has always bothered me, since "Main Screen" is so vague
Only show server value if it differs from cached value
fix opyright date
Add unit test for Horde_Imap_Client_Base_Mailbox
fix viral phpdoc typo
[mms] Add factory for a HashTable instance.
Add Hashtable cache test