[Bitbucket] Unify Server and Cloud implementation

[Spacetown]

Unify the OO implementations:

• Remove checks for "error" in response because an exception is thrown on HTTP errors.
• Moved delete from base class because of the API link. Always returns nothing.
• Moved update from base class because of the API link. Always returns the updated objects (self).
• Add missing link to API documentation always at the end and move existing links. Links always start with "API docs:".
• Fixed relative links in Cloud pull request test mookup and use this links instead of building own links in code.
• Fix update of properties for Server.

[gonchik]

Thank you! :)