Support registration & login with phone number (#742)

* WIP msisdn sign in

* A mostly working country picker

* Fix bug where you'dbe logged out after registering

Stop the guest sync, otherwise it gets 401ed for using a guest
access token for a non-guest, causing us to beliebe we've been
logged out.

* Use InteractiveAuth component for registration

* Fix tests

* Remove old signup code

* Signup -> Login

Now that Signup contains no code whatsoever related to signing up,
rename it to Login. Get rid of the Signup class.

* Stray newline

* Fix more merge failing

* Get phone country & number to the right place

* More-or-less working msisdn auth component

* Send the bind_msisdn param on registration

* Refinements to country dropdown

Rendering the whole lot when the component was rendered just makes
the page load really slow, so just show 2 at a time and rely on
type-to-search.

Make type-to-search always display an exact iso2 match first

* Propagate initial inputs to the phone input

* Support msisdn login

* semicolon

* Fix PropTypes

* Oops, use the 1qst element of the array

Not the array of object keys which has no particular order

* Make dropdown/countrydropdown controlled

* Unused line

* Add note on DOM layout

* onOptionChange is required

* More docs

* Add missing propTypes

* Don't resume promise on error

* Use React.Children to manipulate children

* Make catch less weird

* Fix null dereference

Assuming [0] of an empty list == undefined doesn't work if you're
then taking a property of it.

src/HtmlUtils.js

@@ -58,6 +58,22 @@ export function unicodeToImage(str) {
     return str;
 }
 
+/**
+ * Given one or more unicode characters (represented by unicode
+ * character number), return an image node with the corresponding
+ * emoji.
+ *
+ * @param alt {string} String to use for the image alt text
+ * @param unicode {integer} One or more integers representing unicode characters
+ * @returns A img node with the corresponding emoji
+ */
+export function charactersToImageNode(alt, ...unicode) {
+    const fileName = unicode.map((u) => {
+        return u.toString(16);
+    }).join('-');
+    return <img alt={alt} src={`${emojione.imagePathSVG}${fileName}.svg${emojione.cacheBustParam}`}/>;
+}
+
 export function stripParagraphs(html: string): string {
     const contentDiv = document.createElement('div');
     contentDiv.innerHTML = html;