New gulp debug task and watch CSS folder

[bagage]

Here is a fix for #57 as well as a new target gulp debug so that files do not get uglified when developing.

[nrenner]

Thanks. Don't know how I came to think an additional watch would be more complicated, still had watching CSS on my todo list.

I sometimes use the inject task to insert script tags when debugging doesn't work properly, but then you have to remember not to commit and to revert manually, so the debug option is surely more convenient.