[ZEPPELIN-693] Add AngularJS z.angularUnbind()

[doanduyhai]

What is this PR for?

Add AngularJS z.angularUnbind() method

The signature of the method is angularUnbind(varName, paragraphId).

This is a sub-task of epic ZEPPELIN-635

What type of PR is it?

[Improvement]

Todos

• - Code review
• - Simple test

Is there a relevant Jira issue?

ZEPPELIN-693

How should this be tested?

• git fetch origin pull/741/head:AngularJSUnbind
• git checkout AngularJSUnbind
• mvn clean package -DskipTests
• bin/zeppelin-daemon.sh restart
• Create a new note
• In the first paragraph, put the following code

%angular
<formclass="form-inline"><divclass="form-group"><labelfor="superheroId">Super Hero: </label><inputtype="text" class="form-control" id="superheroId" placeholder="Superhero name ..." ng-model="superhero"></input></div><buttontype="submit" class="btn btn-primary" ng-click="z.angularBind('superhero', superhero, PUT_HERE_PARAGRAPH_ID')"> Angular Bind</button><buttontype="submit" class="btn btn-primary" ng-click="z.angularUnbind('superhero', 'PUT_HERE_PARAGRAPH_ID')"> Angular UnBind</button></form>

• Create a second paragraph with the following code:

z.angular("superhero")

• Retrieve the paragraph id of the second paragraph
• In the first paragraph, replace the text PUT_HERE_PARAGRAPH_ID by the correct paragraph id
• In the input text, put "Superman" and click on the Bind Angular button
• Execute the second paragraph to see that the superhero variable is now set to Superman
• Now click on the Unbind Angular button from the first paragraph
• Refresh the second paragraph to check that the superhero variable has been removed

Screenshots (if appropriate)

Questions:

• Does the licenses files need update? --> No
• Is there breaking changes for older versions? --> No
• Does this needs documentation? --> Yes

[doanduyhai]

@Leemoonsoo
This PR should be straightforward

[Leemoonsoo]

LGTM and merge if there're no more discussions