App checks at startup for an existing session, if there isn't one,
it will start the tool to check for a login in the file:// origin.
If there is one, it will copy the login over to the vector://vector
origin.
In principle this could also be used to migrate logins between
other origins on the web if this were ever required.
This includes a minified copy of the browserified js-sdk with
a getAllEndToEndSessions() function added to the crypto store
(https://github.com/matrix-org/matrix-js-sdk/pull/812). This is
not great, but for a short-lived tool this seems better than
introducing more entry points into webpack only used for the
electron app.
* Turn off node integration in the electron renderer process
* Enable the chromium sandbox to put the renderer into its own process
* Expose just the ipc module with a preload script
* Introduce a little IPC call wrapper so we can call into the
renderer process and await on the result.
* Use this in a bunch of places we previously used direct calls
to electron modules.
* Convert other uses of node, eg. use of process to derive the
platform (just look at the user agent)
* Strip out the desktopCapturer integration which doesn't appear
to have ever worked (probably best to just wait until
getDisplayMedia() is available in chrome at this point:
https://github.com/vector-im/riot-web/issues/4880).
