Overwrite host and webroot when forcessl is enabled

This patch enables the use of forcessl together with a multiple domains
reverse SSL proxy (owncloud/core#1099) which have different hostname
and webroot for http and https access. The code assumes that the ssl
proxy (https) hostname and webroot is configured via overwritehost and
overwritewebroot.
request.php: add type check to the not empty check of a string

The not equal comparison (<>) of a variable with an empty string
could lead to false positive results as the compare do not check
the type and thereby could not make sure that the checked variable
is a string. The usage of the not identical comparison operator
(!==) make sure that the variable is a string and not empty.
fixed xsendfile zip generation race condition
added correct check for gd and check for php-intl
Fix OC_User::getDisplaynames when using numeric user id's

fixes #2948
merge translations with those from theme
merge translations with those from theme
additional safety checks
Priorize common languages.
Make divider not selectable

Very hacky
Cache: only look for child entires when doing a move operation when moving a folder
Cache: add a backgroundjob to check for external changes to the filesystem
Cache: check one folder and one file each time the backgroundwatcher runs

Because there are usually way less folders than files it walks trought the list of all folder quicker, this causes new files to be detected quicker
Use !== and === in user_ldap app – Part 1
Use !== and === in user_ldap app – Part 2
Improve the password reset screen.

Fixing #2752
Fix syntax error.
Don't split translation lines
Oneliners, <br>, proper errors & print_unescaped()
Make class properties protected instead of private to allow subclassing