Closes issue #1005.

- added support for the new Tigris bug tracker in the main website
- added basic documentation about how to develop and test new bug trackers
Fixed tar mission's Quick reference page
Comment out image on 500 error page
Merge pull request #296 from willingc/fix_500error

Comment out image on 500 error page
Hotfix for crashing projects page

We should fix this for real by adding test coverage to urlize_without_escaping_percent_signs()

Also, why does that function even exist?
Revert "Comment out image on 500 error page"

This reverts commit 7b6b3d84f5672dc83a70d4309d9fc632e9f4ec65.

This is important because the Django template syntax does not permit this
comment format.
Better hotfix for failing /projects/

We should stop doing "import *". This seems to be a thing that failed since the
Django upgrade.
Add first draft of docs for quotes database
Remove un-used list trackers button on /customs
Merge pull request #299 from onceuponatimeforever/1013

Remove un-used list trackers button on /customs
Make implicit knowledge more explicit in getting_started doc

Add more clear instructions on how to acquire the oh-mainline source
code.

Closes ticket https://openhatch.org/bugs/issue101
Merge pull request #300 from onceuponatimeforever/install_docs

Make implicit knowledge more explicit in getting_started doc
Fixed #990 Deleted references to geolocation, maps, guessing location

Deleted code in the settings page that has any mention of geolocation and maps,
including geo-location-related html, views, and tests.

Changed default url link "settings" on header from
/settings/location/ to /settings/invite_someone.

Made design decision to re-structure left-hand navigation bar on
settings page in order to improve UI:
    "Tell friend about OpenHatch" tab appears first on top left,
    followed by the "Widgetize yourself" tab, and finally,
    the "Email", "Name", and "Password" navigation tabs.

Made design decision to have the message "If you want us to forget your
location, empty out the text field and hit save" appear as the default
location message in settings page.
Merge pull request #273 from onceuponatimeforever/990-new

Fixed #990 Deleted references to geolocation, maps, guessing location
Fixed closing p tag in line 42
Merge pull request #295 from eeshangarg/bug-1008-fixed-tar-mission-reference-page

Fixed tar mission's Quick reference page
Use Oppia explorations for the tar mission.
Tick the progress boxes on completion of the step.
Remove tests that are no longer required. Fix other failing tests.
Remove unused code.