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
Add blend method widget into gradient tool options panel.
Improve UI layout of Options.

1. Options Panel border width set to 3px
2. Row spacing is 5px
3. Widgets spacing in the same row is 3px
4. Spacing of sub-option widget is 8px
Add(uncomment) blend method wiget for Circle Tool Options Panel
Add opacity widget to circle tool options panel.

It is still a global wide widget, should be changed to a local option which
affects circle tool only.
Add brush size widget to circle tool options panel.

It is still a global wide setting, should be changed to affect
circle tool only.
Remove comment
Replace checkbutton with togglebutton for layer creation
Improve labels and add some missed labels
Pack all layer type in a hbox

- Pack all layer creation buttons in a hbox,
- Pack  Name and its text field in an other hbox,
- Align Title label to left.
Align Checkbutton items

Checkbox at the right and its label at the left
Don't expand layer creation buttons.
Order options