Tidy up file structure

Teaching notes:

> mkdir client collections lib public server
> mkdir client/views client/stylesheets
> mv cherry-tomato.html client/main.html
> mv cherry-tomato.css client/stylesheets/main.css
Create new files:
  > touch client/main.js
  > touch server/main.js
  > touch collections/pomodoro.js
  > mkdir client/views/pomodoros
  > touch client/views/pomodoros/pomodoros_list.html
  > touch client/views/pomodoros/pomodoros_list.js
move templates from main.html
move contents of cherry-tomato.js
> rm cherry-tomato.js