Add delete button for actions

[diananova]

• Feature description: (Example: Add an exit button)
  Allow the user to delete an action.

• Reason for the feature or improvement: (Example: there is no right way to exit from the application)

• How does your idea fit with the aim/scope of the project? (Example: feature gives the workflow)

• What are the merits of the feature? (Example: prevent data loss)

• Screenshots, if you can show something similar, or a sketch:

• Any other information:

[diananova]

#17 initial setup: HTML button, add click event.
next step: implement deleteAction() function.
** also cleaned up drawSubgoal() function, as there was a lot of duplicated code.