Refactor markdown-textarea component into ember-cli addon

[achan]

Read: http://www.ember-cli.com/#developing-addons-and-blueprints

Convert the markdown-textarea component created in #10 into a dedicated ember-cli addon so that other people can reuse/import the component in their projects.

Try to keep the code design consistent with https://github.com/plusacht/ember-bootstrap-datetimepicker.

• create new addon in new git repository ember-cli-bootstrap-markdown
• rename the component to bs-markdown-textarea
• remove old markdown-textarea component from mcac-js
• import new ember-cli-bootstrap-markdown into build via ember-cli