161 - Align rows of Params Panel and Timetrack Panel - Progress

- Affect a widget to the first column to retrieve it when style is updated
161 - Align rows of Params Panel and Timetrack Panel - Progress2

- remplace LayerTree::param_tree_columnzero_label member to create it dynamiclly
- connect param_tree_view().column(0)->widget style_changed signal (from Gtk::Widget)
to studio::LayerTree::on_param_tree_column_label_style_changed)
- connect param_tree_view().column(0)->widget expose_event signal (from Gtk::Widget)
to studio::LayerTree::on_param_tree_column_label_expose_draw)

- add commented adhoc gtkmm3 functionnaly for style_changed (style_updated) and
for expose_event (draw)
161 - Align rows of Params Panel and Timetrack Panel - Progress3

- add bool LayerTree::update_param_tree_header_size() member
and associated int ayerTree::param_tree_header_size.
161 - Align rows of Params Panel and Timetrack Panel - Progress4

- Add sigc::signal<void,int>& LayerTree::signal_param_tree_header_size_changed ()
161 - Align rows of Params Panel and Timetrack Panel - Progress5

- add Dock_Timetrack::on_update_header_size( int header_size) member
- connect Dock_Timetrack::on_update_header_size to studio::LayerTree::signal_param_tree_header_size_changed
161 - Align rows of Params Panel and Timetrack Panel - Progress6

- update the widget_timeslider and widget_kf_list on update_header_size
Fix-161 - Align rows of Params Panel and Timetrack Panel

- change reference to size by height
- add Dock_Curves::on_update_header_height( int header_height) member
- connect Dock_Curves::on_update_header_height to studio::LayerTree::signal_param_tree_header_height_changed
- update the Dock_Curves's widget_timeslider on update_header_height
- update comments
Merge pull request #119 from d-j-a-y/djay_align_rows

Partially fix #161 - Align rows of Params Panel and Timetrack Panel