Replaced build.sh with Makefile
Warn and cope if uglifyjs is not installed.
Add 'make source' feature

'make source' builds a version of bungee.js which acts a loader.
Real bungee source code files are fetched at runtime. This helps
development as changes in bungee source code files become visible
immediately.

'make [build]' swithes back to static concatenated bungee.js
file which is only updated after next 'make [build]' command.
Merge pull request #1 from ilkkao/master

Building related improvements