Remove deprecated link checker metric controller

Due to the link checker metric controller I was not able to start
Sidekiq anymore. This was no problem, since I need to remove the
controller anyway. Also changed the JavaScript requirement to the
minimized version.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Restore Sidekiq middleware

Another victim of the Rails 4 upgrade was the Sidekiq middleware
initializer. Properly this is also the reason why the status was
not served anymore. This commit restores the file.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Restore name method to the metric base class

I have re-added the name method of the metric base class. Now it is
simply based on the to_sym method of the class.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Fix success determination for response code

I used the (and) operator which has a lower precedence than the
assignment operator (=), hence I have replaced it with the (&&)
operator.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Improve link checker by adding HTTP 4xx case

A HTTP 4xx client error is sometimes an indicator that the header
request method is not supported by the server side. In this case
I am running a complete get request. In addition, I have raised
the timeout and connection timeout.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Remove follow location implementation

Since the library provides already a follow location option I do not
need to implement this myself. I have removed the code and also added
the option to not verify the SSL peer.

In addition, I have changed the (un)escaping of the URL once more as
well as adding checks to prevent exceptions if the worker is undefined.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>