Add "Pomodoro mode"

[igrybkov]

Settings

• Add ability to set time interval used for Pomodoro session
• Add ability to set time interval used for a short break
• Add ability to set time interval used for a long break

Time intervals

• Does not show time interval selection since we have time interval already predefined
  • This would require to add a filter between "Choose a task" and "Choose a time" and skip time setting in case a time is set already

Tasks flow

• When time is gone, a pomodoro is logged

Logging

• Each Pomodoro must be logged somewhere to build a report later
  • Think about where and how you're going to log these pomodoros
• Build a report
  • How are you going to build report around Pomodoros?
    • Build a PDF with report?
    • Excel?
    • Small web-server and a page?
    • A page in the PDF?
  • What should report contain?
    • Number of pomodoros accomplished
    • What else?

Related issues

Depends on ability to manipulate with workflow settings (#47)
Pomodoro reminder depends on #1 where reminder functionality should be added
Potentially crosses with task pausing implementation (#48) - at least they should be checked together