misc: add helper make dev command

Running webpack-dev-server is not enough, so add a helper which takes are of
doing the needful.

Makefile

 STYLES_DESTINATION = css/all.css
 STYLES_MAIN = css/main.scss
 WEBPACK = ./node_modules/.bin/webpack
+WEBPACK_DEV_SERVER = ./node_modules/.bin/webpack-dev-server
 
 all: compile deploy clean
 
 deploy-local:
 	([ ! -x deploy-local.sh ] || ./deploy-local.sh)
 
+dev: deploy-init deploy-css deploy-lib-jitsi-meet
+	$(WEBPACK_DEV_SERVER)
+
 source-package:
 	mkdir -p source_package/jitsi-meet/css && \
 	cp -r *.js *.html connection_optimization favicon.ico fonts images libs static sounds LICENSE lang source_package/jitsi-meet && \

README.md

 make
 ```
 
-## Working with the library sources (lib-jitsi-meet)
+### Working with the library sources (lib-jitsi-meet)
 
 By default the library is build from its git repository sources. The default dependency path in package.json is :
 ```json
 ```bash
 cd lib-jitsi-meet
 
-# create global symlink for lib-jitsi-meet package
+#### create global symlink for lib-jitsi-meet package
 npm link
 
 cd ../jitsi-meet
 
-# create symlink from the local node_modules folder to the global lib-jitsi-meet symlink
+#### create symlink from the local node_modules folder to the global lib-jitsi-meet symlink
 npm link lib-jitsi-meet
 ```
 
 npm unlink lib-jitsi-meet
 npm install
 ```
-## Running with webpack-dev-server for development   
+### Running with webpack-dev-server for development
 
 Use it at the CLI, type
 ```
-node_modules/.bin/webpack-dev-server
+make dev
 ```
 
-By default the backend deployment used is `beta.meet.jit.si`, you can point the Jitsi-Meet app at a different backend by using a proxy server. To do this set the WEBPACK_DEV_SERVER_PROXY_TARGET variable, type 
+By default the backend deployment used is `beta.meet.jit.si`, you can point the Jitsi-Meet app at a different backend by using a proxy server. To do this set the WEBPACK_DEV_SERVER_PROXY_TARGET variable:
 ```
-WEBPACK_DEV_SERVER_PROXY_TARGET=https://your-example-server.com node_modules/.bin/webpack-dev-server
+export WEBPACK_DEV_SERVER_PROXY_TARGET=https://your-example-server.com
+make dev
 ```
 
 The app should be running at https://localhost:8080/
 
 The Jitsi Meet architecture allows you to deploy your own version, including
 all server components, and in that case your security guarantees will be roughly
-equivalent to these of a direct one-to-one WebRTC call. This is what's unique to 
+equivalent to these of a direct one-to-one WebRTC call. This is what's unique to
 Jitsi Meet in terms of security.
 
 The [meet.jit.si](https://meet.jit.si) service is maintained by the Jitsi team