Revert "Close #496 Set travis git clone depth to 1"

The problem with using git clone depth 1 is that if the contributer
pushes multiple commits in short succession before Travis is able to
kick off a build. The build will fail due to being unable to find the
commit. This is because Travis checks out a branch and then checks out
the exact commit. So it is possible to get into a situation where the
latest branch is newer than the commit Travis is trying to build
against.

This reverts commit 217a887c2341ffa4bf12e7fc29bbf6335436ae5d.
Add *.egg/ directories created by pytest

Signed-off-by: Thanh Ha <thanh.ha@alumni.carleton.ca>
Ignore PEP8 E265

Signed-off-by: Thanh Ha <thanh.ha@alumni.carleton.ca>
Fix E714 test for object identity should be 'is not'

Signed-off-by: Thanh Ha <thanh.ha@alumni.carleton.ca>
Fix #523 Add New Talk button should open a popup for editing the new talk

- Add NewTalkWidget class which has its own instance of TalkDetailsWidget
- Add instance of NewTalkWidget to TalkEditorApp and display it as a modal
  dialog when Add New Talk button clicked
- Add new talk to database when Add button clicked, close dialog and refresh
  table view
- Set appearance of dialog (title, size, button placement, placeholder text,
  date format)
- Add docstrings for show_new_talk_popup and refresh_table functions