use pygal to output chart and simplify sprint-burnup command
remove debug leftover
remove unnecessary code
Revert "remove debug leftover"
(actually not debug...)

This reverts commit 04732ba8089865af4261dfe5bc3c0d96b8243aa9.
output graph in output_dir selected by user
output only used series and improve layout
css hosted on github, some layout improvements
improve style
add velocity
major refactoring: separate more clearly commands/managers/remotes/models
remove unnecessary code
helper to get zebra/jira managers in commands
rename ZebraEntry to TimeSheet, JiraEntry to Story, JiraEntries to StoryCollection
refactor models
add method to gather all days between a start and end dates (excluding or not weekend days)
clean the planed time parser
respect graph_end_date
use pygal for result-per-story
refactor output
add actual/planned as text for each story on result-per-story graph