Changes in this commit:
- updated head to include local jquery
- put mins and secs into their own html elements
- removed onclick from buttons, becaused added click events via js
- set default start time in the html (at 3 mins)
- created onready which registers click events to start and stop buttons
- created start and stop methods
- changed countdown to use recursive function, checks for global
  'paused' variable to break loop
- refactored code for additional clarity
- implemented start/stop functions
- separated some content from the javascript code (e.g. 'time remaining'
  message)