Remove `vscode:prepublish` and split `build` and `package` scripts

[thetarnav]

The vscode:prepublish script were causing compile script to be executed twice when running npm run package.

Also I've split package to build and package so that the extension can be quickly rebundled when I've only changed the grammars.

$ npm run package

> ols@0.1.16 package
> npm run compile && vsce package -o extension.vsix

> ols@0.1.16 compile
> tsc -p ./

Executing prepublish script 'npm run vscode:prepublish'...

> ols@0.1.16 vscode:prepublish
> npm run compile

> ols@0.1.16 compile
> tsc -p ./

This extension consists of 288 files, out of which 211 are JavaScript files. For performance reasons, you should...