merge "challenges-dev" into "gssoc20-dev"

[eshaan7]

New features:

• Multiple boxes support (closes issue Support for n number of boxes #17)
• Challenges page (closes issue Challenges page similar to machines #56). Along with tag and category models for organization.
• CTF settings and websites are now stored in database and can easily be changed from the new /setup view. (Closes issue GUI control of config.py CTF settings #55)
• WTForm class for Machine for editing/creating new machines.
• Implemented thorough and efficient caching with use of "Flask-Caching" and "Redis".
• Now uses flask factory app method so the various flask extensions can be well-managed.

Changes:

• Define redis service in docker-compose.yml
• Redis add-on has been added to app.json.
• ADMIN_EMAIL, and mail related env variables added in app.json.
• Flag submission is now in a modal.
• DB models are now in their respective folders in models.py
• Optimized scoreboard's detail fetching
• Features such as searching and exporting and new dark theme for Admin Controls (closes issues Admin Controls, Settings #1, "Admin Controls" - Dark theme #16, Improving the admin controls interface #36 )
• Some utility functions such as @admin_only decorator.
• macros have been defined in templates for reusability.

[lgtm-com]

This pull request introduces 5 alerts when merging 0f5157b into 1405748 - view on LGTM.com

new alerts:

• 5 for Cyclic import

[lgtm-com]

This pull request introduces 3 alerts when merging 5cf7d97 into 1405748 - view on LGTM.com

new alerts:

• 3 for Wrong name for an argument in a call

[lgtm-com]

This pull request introduces 2 alerts when merging c77dcfa into 1405748 - view on LGTM.com

new alerts:

• 2 for Wrong name for an argument in a call