/upload handler and storage database

* Add API for querying the state after a list of events

* Implement state after events API

* Actually implement the API

* Reorder .travis.yml

* Comments

* Use common.MakeAPI

Content-Disposition is only used for communicating the filename. It does
not need to be stored in the database as we have upload_name anyway. It
does not need to be in types.MediaMetadata and does not need to be
logged.

Reorder functions to have public API functions in alphabetical order at
the top, internal package functions at the bottom in call order.

Use RawURLEncoding to avoid padding the hash with '='.

Use stronger types for paths in public API.

Simplify comments.

Skeleton for the Media API

Content-Disposition is not a valid request header and so it must be
evaluated from the upload request's filename query parameter.

Clearer that it's a map from mxc URLs to sync.Cond

* Start implementing the join room API

* Hacks to get join room working

* Make the TLS fingerprint configurable

* Fix the client API proxy to handle '#' correctly

* Return a 200 OK response

* Write the join event along with current state to the room server

* Comment on the error handling

* Fix typos

* Fix tab

* Add TODO for moving authEventIDs to gomatrixserverlib

* Comment on why we ignore the key ID argument for local keys

* Avoid 'preceeded'

* Neaten the control flow

* Neaten the control flow even more

* Return pointers

* Rename err to lastErr for the loop

- Renamed `clientapi/auth/types` to `clientapi/auth/authtypes` for the same
  horrible namespace clashing reasons as `storage`.
- Factored out `makeAPI` to `common`.
- Added in `makeAuthAPI`.