Remove alert link underline

There is a double-underline when links appear in the alert. This
removes the default underline.
Merge pull request #579 from codeforamerica/remove-alert-link-underline

Remove alert link underline
Fixes minor haml style guide offense
Refactors clear button

- Removes redundant element lookups.
- Adds checks for if reset was called before initialization and throws
error if they weren’t.
- Adds additional code comments.
- Updates class names to be more descriptive (“clear” instead of
“close”).
Merge pull request #580 from codeforamerica/clear-all-button

Clear all button
Merge remote-tracking branch 'upstream/master' into upstream-updates
Updates precompiled assets