Add issue tracker's support

[w32blaster]

Add interface and different realizations for issues trackers. Revizor should be able to scan a commit description and extract URL or Key of an assigned ticket. The link should appear in a review description.

Dod:

• [x] if Smart Commits are presented in a comment description, then:
  • [x] an upcoming review should be associated with the given Issue
  • the header and description should be pre-filled when an user creates a new review
  • [x] the Issue itself should be modified: in simpliest case append to its description link to review. Otherwise some trackers (like Jira) have special link for a code reviews.
• [x] an user should have opportunity to assign manually any Issue to already existing Review
• [x] when some actions happen in a review (approve/disapprove, closing, comments) then an appropriate comment should appear under the associated Issue.
• [x] add cache to the remote calling

  Issue trackers to be supported:

• Jira
• YouTrack
• GitHub Issue Tracker
• BitBucket

[w32blaster]

the example of how to keep regex in variables:

def prefix = "tim_"
def prefixPattern = "${prefix}*.*"

assert    "tim_woo" ==~ ~/${prefixPattern}/

[w32blaster]

API for GitHub: https://developer.github.com/v3/issues/

[w32blaster]

Bitbucket API: http://restbrowser.bitbucket.org/

[w32blaster]