Replace the current timebar with a new timebar widget (v2)

Replace the current timebar with a new timebar widget (v2)

Create a timeentry GtkWidget to manage the entry of a seconds/nanoseconds value
Create a timebar GtkWidget which aggregate 4 timeentry (Start, end, current time
+and time interval)
Simplify the main window tab widget code by using this new timebar.
Changelog:
 Fix crash in time pasting and spacing adjustment of widgets
 Fix interval management when pasting to keep a coherent time
 Rework the signaling management

Signed-off-by: Yannick Brosseau <yannick.brosseau@gmail.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>