fixes #9101

Removing this doesn't affect the controls bar visually but does affect
the breadcrumb calculation when getting available width.

- serve CSS and font files properly to make sure that measurements are
  correct for the tests that need them (breadcrumb)
- added opacity to testArea to make sure nothing is visible during
  testing

In case the filepicker function is called twice, only show it once.

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.