When using big session timeout values, the interval value might
overflow and cause the setInterval() call to ping the server in a loop
without any delay.

This fix adds a maximum ping interval of 24 hours.

Forward port of 00ec5fc1935c946e846a8ff28491e5b5b017b3d7 from stable6.

The updater is using "before update" repair steps and "regular" repair
steps.
The "regular" repair steps are also used by the CLI tool.

Currently no steps exist but can be added later in the static methods in
the \OC\Repair class.

Added unit test to test messaging, error and exception cases.

This also makes it possible to unit test each repair step class
individually

Fix #8996

Snapper doesn't work at all for IE8 and IE9 and messes up with the main
container layout when enabled.

This commits disables snapper for these browsers.