A few improvements, including downloading photo

[igubanov]

this pr add some changes/fixes/improvements each commit change something independent:

• added requirements file for fast installing required dependencies
• skip 401 error (sometime Jira Server return it for some tikets instead of 404) and add related issues to missing
• add authentification to Jira Server with OAuth token (Bearer token without login)
• add dowloading user avatars
• add json_issue to skipfilter method (for building skip rules by issue fields)

[rybak]

Thank you for your interest in jira-gource. Unfortunately, I won't have time this week to review your pull requests. I'll try to find time next week.