Tune queue indicator

This MR rework the task queue indicator in order to have a better feedback.

Closes #48 (closed)

This MR is a proposal to rework the queue icon status.

• Use a cog glyph instead of a database glyph
• Display the amount of queued jobs
  • Now the main icon displays the pause/stop symbols
  • The running job is not counted as a queued job
• The indicator is red except when the queue is not ready
• Animate the main icon when something is processing (to make it really visible)
• Rework the tooltips
  • Display the number of queued job