Small performance improvement on imap_open

Use the OP_HALFOPEN flag to reduce server load. We don't need to open a mailbox, so just don't try
I've also make the check clearer for the opened connection (I know, 2 PR in one, it's bad…)
Fix untranslatable strings in first run wizard

This should help some languages to translate those
two lines correctly.
Fix jQuery selector for checkboxes so the settings work again
Merge pull request #1735 from owncloud/fix-activity-settings

Fix jQuery selector for checkboxes so the settings work again
[tx-robot] updated from transifex
[tx-robot] updated from transifex
[tx-robot] updated from transifex
Merge pull request #1734 from wakeup/master

Fix untranslatable strings in first run wizard
[tx-robot] updated from transifex
[tx-robot] updated from transifex
[tx-robot] updated from transifex
[tx-robot] updated from transifex
Merge pull request #1723 from Glandos/patch-1

Small performance improvement on imap_open
Add activities for shared users when a file is added or deleted

Fix #1670
Fix activities and links when folders and files are shared:
* When sharing via link, the activity link leads to the user's root instead of the folder
* When sharing an item with a user, the links always lead to the new user's target folder
* When sharing an item with a group, an activity was created for the group
Do not loop over all shares unneccessarily
Fix sharing an item with a group
Do not add activities for .part files

Fix owncloud/core#7950