Refactors map to use marker manager

- Moves map icon management to its own module.
- Update marker icons to be more consistent with forks that have
differentiated map markers.
Updates stack versions in readme

Updates Ruby & Rails stack versions in readme to latest used versions.
Update compass-rails to 2.0.0

- Updates compass-rails to 2.0.0
- Updates compass to 0.12.7
Merge pull request #557 from codeforamerica/map-manager-refactor

Refactors map to use marker manager
Merge pull request #559 from codeforamerica/update-readme-stack

Updates stack versions in readme
Merge pull request #560 from codeforamerica/update-compass

Update compass-rails to 2.0.0
Updates map marker filename

Changes underscore to hyphen to be consistent with file naming
convention in other modules.
Adds applicationjs to all routes

application.js was excluded from the result and detail view routes.
This adds it to all route modules.
Merge pull request #563 from codeforamerica/applicationjs-all-routes

Adds applicationjs to all routes
Update default location text. Closes #554.
Merge pull request #566 from codeforamerica/554-default-location-text

Update default location text. Closes #554.
Adds right-hand padding on text input filters

Fixes #562 - adds right-hand padding on text input filters.
Merge pull request #568 from codeforamerica/562-input-padding

Adds right-hand padding on text input filters
Improve page caching & add documentation.

- Disable page caching by default and enable it via the
`ENABLE_CACHING` env var.

-  Don’t cache no results page.
Update and simplify caching documentation.
Merge pull request #570 from codeforamerica/fix-caching

Improve page caching & add documentation.
Update caching documentation.
Merge latest updates from upstream.
Precompile assets locally.