[18.0] web_view_leaflet_map : add 'Create' missing button

[legalsylvain]

[REF] web_view_leaflet_map: full refactor.
- rename folder to follow odoo and OCA conventions, regarding views definition
- isolate leaflet_map_view code
- isolate leaflet_map_controller code
- isolate leaflet_map_renderer code
- split xml file into renderer and controller part
- apply Odoo SA convention

[FIX] remove useless logs, and put a single one in debug level
- remove useless code
- remove obsolete directive: control-panel-bottom-right

[IMP] web_view_leaflet_map: introduce 'Create' Button

Before

After

[legalsylvain]

CC, recent contributors / reviewers : @mourad-ehm @thibaultrey, @tate11, @NL66278

Note : I investigated a little, regarding the possibility to add a search bar (Ref: #419 (comment)), but it requires a full refactoring, because pointers rendering are not done in a classic "odoo" way for the time being.

Also ideally, we should make a dynamic filter, to avoid to load records that are "out" of the displayed map. (for the time being, the map size will be adapted, depending on the records.