Convert main build command into a proper rule
Unhide version generation command
Let make call 'go get' when needed

List all non-standard dependencies and look for them all under $GOPATH.
If any of them is missing, run 'go get'.
Let make call 'npm install' when needed

Check node_modules for presence of dependencies and call 'npm install'
only if needed. Similarly, call 'bower install'.
deploy: regenerate src/version.go

Make sure the build for deployment has the latest version.go.
Remove a few build instructions from README

They're all handled automatically by Makefile now.
Don't copy js/*.js to output
Add golang-go.tools to dev-packages
Avoid npm warning: add repository field
Copy server.conf only if the source is present

server.conf is not checked in to source control, it's only for my
convenience.
Improve build instructions in readme
Generate version.go as the very first step

I've encountered a 'go get' failure on a clean build. Not sure why would
that happen, but let's try to prevent that.
Show a nicer message while 'go get' runs
Simplify Travis config, let make do all the work