Issue page update

Features:
    - Complete issue page redesign.
    - Now issuepage is divided into columns: issue info, branch tree & info, solutions. This is a much clearer layout.
    - Branch & solution creation is made through a simple form.
    - Fixed a lot of bugs, especially regarding filepaths and stuff in the API.
    - Subdomains work now.
    - Buttons are redesigned
    - Branches can now be assigned a priority (Very relevant, Relevant, Not relevant)
    - Session deletion fixes.