Renamed a few methods to be more consistent

(As previously discussed with @tilgovi)

Sidebar -> Document RPC methods:
 * Renamed `scrollTo()` to `scrollToAnnotation()` (to be consistent with `focusAnnotations()`

Guest methods:
 * Renamed `showViewer()` to `showAnnotations()` (to be consistend with `focusAnnotations()`)
 * Renamed `updateViewer()` to `updateAnnotations()` (same reason)
 * Renamed `toggleVIewerSelection()` to `toggleAnnotationSelection()` (same reason)
Merge pull request #1750 from hypothesis/more-consistent-names

Renamed a few methods to be more consistent
Rename rpc methods to be more consistent

Between guests <-> sidebar
- `showViewer()` to  `showAnnotations()`
- `updateViewer()` to `updateAnnotations()`
- `toggleViewerSelection()` to `toggleAnnotationSelection()`

All these renames were to enforce encapsulation and these calls
are more like APIs. To guest side really do not have to know anything
what the sidebar has or does.
Consolidate code paths around deciding about PDF.js

Annotator's PDF.js plugin replaces the document plugin
for PDF.js, so when we are using the PDF plugin, we
don't want to load the document plugin.

For this, we are removing it from the options, in
presence of PDF.

This commit changes how we test for PDF.

Earlier, we were simply testing for the presence of the
global PDF.js object, but it's better to actually
use the test already implemented inside the PDF plugin.

This has two benefits:
 * If the PDF plugin is not present, we won't
   mistakenly  remove the document plugin.
 * If the PDF plugin decides that it can't deploy,
   for whatever reason, we won't
   mistakenly remove the document plugin.
Merge pull request #1752 from hypothesis/consistent-rpc-names

Rename rpc methods to be more consistent
Load the PDF or the Document plugin conditionally
Merge pull request #1753 from hypothesis/better-pdf-test

Consolidate code paths around deciding about PDF.js
Fix double loading on install

This issue arises because we're not checking the status of the tab
before trying to inject. So when during installation a new tab is
created and the extension activated this triggers the change from
'inactive' -> 'active' in TabState which embeds the sidebar into the
loading tab. Later the update function is called when the tab loading is
complete injecting the sidebar a second time.

We now explicitly check the tab status in the injection handler to
prevent injection into a loading tab.

Fixes #1756.
Don't use target="_blank" for feedback email
Correct spelling
Merge pull request #1761 from hypothesis/feedback-target-blank

Don't use target="_blank" for feedback email.
Rename Heatmap -> BucketBar

Ref #1236
Merge pull request #1767 from hypothesis/rename-heatmap

Rename Heatmap -> BucketBar.
Remove unused dynamic bucket code
Merge pull request #1768 from hypothesis/remove-dynamic-bucket

Remove dynamic bucket from BucketBar
Move thread conditionals onto top level element

Rather than the thread-reply and thread-load-more elements having
one set of conditions on the parent and one on the child we now ensure
that the entire element is always shown/hidden.
Merge pull request #1758 from hypothesis/1756-double-load-on-install

Fix double loading on install
Merge pull request #1770 from hypothesis/thread-display

Move thread ng-show conditionals onto parent elements
Include h automatically when creating the app
Update api.rst