Autoyast support + code improvements

This is a quite big PR, but for AY support I needed to share some code between standard client and AutoYast client. Therefore I moved the dialogs to separate files, added more tests and added some improvements.

- Many dialogs were moved so separate files
- UI Workflow definitions as well
- Added HTTP redirection support in download code
- Allow specifying SSL certificate fingerprint in AY, the certificate is imported when the fingerprint matches (no need to to download the certificate via a side channel)
- Download and import SSL certificate during AY installation (backward compatibility with old registration)
- Download available addons from server in AY config mode (if the system is registered)
- Install addons in AY installation
- Created `SslCertificate` class for certificate related code
- Added [Inch CI](http://inch-ci.org/) support for checking `yardoc` comments
- Splitting the classes and methods improved CodeClimate mark by [+0.39 (from 2.1 to 2.49)](https://codeclimate.com/github/yast/yast-registration/compare/autoyast_support)
- Enabled only the new RSpec syntax in tests, fixed the old style
- Added tests increase code coverage by +4.8%
- The AY RNC schema has been updated
- Implemented "Modified" flag, registration is skipped during clonning (bnc#888168)

<small>*Sorry for such a big PR, I should have asked for review continuously...* :pensive: </small>
it is quite too nested and confusing for me. better to structure like
```
it "returns 'regurl' boot parameter from Linuxrc if specfied"
...
it "continues to return the SLP server selected by user if SLP server is anounced"
...
it "continues to return the nil user select cancel during SLP dialog"
...
it "returns nil in other cases"
```