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Separate session/helpers bundles, tweak bundling

Tweak the way we organize our asset bundles for fewer output files,
straightforward names, and no conflict of dev and prod output files.

- Break session and helpers into their own bundles.

- Bundle vendor libs up where they are not common to more than one
  optional component. For example, angular-bootstrap is only needed by
  helpers since that is where we now redefine tabbable and create
  the tab-reveal directive (in a new helpers/ui-helpers.coffee file).
  Another example is angular-resource, which is only used by the session
  bundle. On the other hand, angular-route is used by the app, but soon
  also by the auth bundle as soon as we unify all the login forms and
  boot out deform.

- Inline icomoon.css.

- Rename some outputs:
  - hypothesis-app.{css,js} -> app.{css,js}
    This is the main site application.
  - hypothesis-inject.{css,js} -> hypothesis.{css,js}
    This is the inject script.

Close #1555
Related to webplatform/notes-server#13
Add myself to AUTHORS
Revert "Limit the markdown toolbar for tight spaces"
Change icon prefix to h-icon to reduce conflicts

This should reduces the chances of style conflicts when annotator
content is injected into a host site. This pull request also ensures
all icons use the private use area of the unicode range[1].

[1]: http://en.wikipedia.org/wiki/Private_Use_Areas
Update all icon references to use the new namespace
Add an icons mixin for working with icomoon classes
Remove specific icon class from toolbar stylesheet

This allows the icon name to be changed freely without having to
update unrelated markup or stylesheets.
Remove specific icon class from markdown stylesheet
Remove self closing tags from markdown template.

Only a subset of elements are self closing[1].

[1]: http://www.w3.org/TR/2011/WD-html-markup-20110113/syntax.html#void-element
Clean up nested link styles in annotator-toolbar

Previously this generated a large amount of invalid unused css due to
nesting pseudo classes.
Namespace the pushed class in the annotator-toolbar

This will reduce the chance of styles bleeding in from the parent
document.
Rename icon-checkmark2 to icon-checkmark
Fix margins jumping when toggling cards

Close #1412
Merge pull request #1554 from hypothesis/hide-tags-in-collapsed-reply-threads

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Merge pull request #1559 from hypothesis/fix-icon-conflicts

Fix icon conflicts
Merge pull request #1557 from hypothesis/1555-asset-bundle-structure

Separate session/helpers bundles, tweak bundling
Fix icon classes with missing h- namespace
Hide lock icon next to username when editing
Merge pull request #1561 from hypothesis/fix-1538

Hide lock icon next to username when editing.