PROD-1070 - Fixes Anchor Tags on Firefox

**Status**: Review
**Review**: @jansepar 
**JIRA**: [PROD-1070](https://mobify.atlassian.net/browse/PROD-1070), [PROD-1155](https://mobify.atlassian.net/browse/PROD-1155)

## Changes
- (On Firefox) Adds an event handler to every link that properly handles anchor tags, and patches up `preventDefault` anchor scrolling can be cancelled by the usual methods (returning `false`, calling `preventDefault`, etc).
- Adds tests (for all browsers) to test that anchor tags behave properly
 
## How to test-drive this PR
- Run the tests
- If you need you to manually test it, visit http://localhost:3000/tests/fixtures/anchor-test.html and tap the links.
 
## Notes
On Android 4.0.x, iFrames don't behave well with scrolling and anchor tags. However, manually testing shows that it works on 4.0.x.

## Todo
 - Test on Android 2.x
 - I'm not sure where we should put this patching code. There isn't an obvious place to put it so it runs after capturing, without requiring the user to explicitly add the patching code themselves.