Gruntfile: Restructuring.

[timwienk]

Structure:

Gruntfile.js:

• configuration of basic environment;
• loading files with more specific options;
• loading tasks.

Grunt/options/*.js:

• configuration options split by target.

Grunt/options/browsers.json:

• browsers used as customLaunchers for karma.

Grunt/plugins/*:

• plugins used in/by the grunt tasks.

Grunt/tasks/*:

• registration of tasks.

  Notable changes:

Gruntfile API:

• renamed "all" and "default" builds to the more clear "compat";
• new "travis" task, takes care of travis specific stuff;
• new "test" task, runs all tests (including server tests);
• new "default" task, runs either the "travis" or "test" task.

Other changes:

• built files now end up in a "build" directory (or "dist", of course);
• removed server-tests.js in favour of grunt-mocha-test package;
• updated the browser list (most notably: added edge);
• updated .travis.yml to use updated browser list;
• updated .travis.yml to use new "compat" build, instead of "default";
• moved syn karma-plugin into Grunt directory;
• updated and cleaned up .gitignore;
• removed no longer used packages from .package.json;
• updated README.md (some parts were actuall already out of date).

  Travis-CI tests

• Normal build: https://travis-ci.org/timwienk/mootools-core/builds/83433722
• Pull Request: https://travis-ci.org/mootools/mootools-core/builds/83433649

[SergioCrisostomo]

:+1: nice work!