[#6] User can edit and delete tasks.

1. Added a button with pencil glyphicon to each task that shows on hover. click it to open the taskModal
2. Added taskModal for updating and deleting tasks.
3. Added event handler to task item edit button to open taskModal.
4. Created form for taskModal.
5. Added event handler for submitting form in taskModal
6. Added event handler for deleting task in taskModal