Initial pass at catching an invalid identity crisis caused by wp-config

Initial pass aimed at updating the identity crisis check to include a check for constants
that can be defined in wp-config that will cause a mismatch between the url wpcom expects
the wporg site to have and the actual url used. Potentially fixes #1006
Fix oops on continue always firing
Likes: display below excerpts as well

Before this commit, Likes were only displayed below the_content
Sharing buttons, on the other hand, are displayed everywhere

Both modules should have the same behaviour
Likes: do not hide Likes for excerpts

See #484
Likes: remove $wp_current_filter

It's not necessary anymore now that we don't check for excerpts
Vimeo Shortcode: add the autoplay parameter
Merge pull request #484 from jeherve/likes-excerpt

Likes: display below excerpts as well
General: Bugfix when jetpack was updated, all modules were disabled except for the new auto activated module
Add tests for id crisis check.
Fix id crisis force ssl check.

Check constant definedness properly. Made the function an instance method, because why not, and easier stubbing.
Merge pull request #1021 from Automattic/id-crisis

Resolve identity crisis when using FORCE_SSL_ADMIN
Tidy up some logic around button displays

Don’t display a button for a user to connect their user account if the
blog itself isn’t connected yet.

Props @koke for finding.
Added some more Jetpack_PostImages unit tests.
Vimeo: allow for all non-empty parameters to trigger autoplay
Change how we're flagging new modules

Old way would catch modules introduced in `1.1` during version `3.1.1`
— this way shouldn’t, while still accounting for `3.1` being new in
`3.1.1` and `3.1-dev` and `3.1-beta1`

Props @beaulebens for the bug report.
Merge pull request #1019 from jeherve/add/vimeo-autoplay

Vimeo Shortcode: add the autoplay parameter
Partial revert of a path change.

@see
https://github.com/Automattic/jetpack/commit/bdfc92311418#diff-287b3ba61
d50d9095f9f4dea66d2061fR22

This is the wpcom path, and only happens if we’re not in Jetpack which
overrides correctly to _inc.
REST API: 400s should return regardless of origin…

…so that oauth errors can be caught by developers.

Props @jkudish
Merges r102728-wpcom
REST API: Add 'plugin' type to cast_and_filter_item.

Used to cast and filter the result of the list plugins endpoint.
+ Add 'safehtml' type applies wp_kses to the response value. Used to sanitize the plugin description.

Merges r101961-wpcom.
REST API: Add 'jetpackmodule' type.

Used to safe cast the module description.

Merges r102179-wpcom.