Enable fast and GUI controllable alphabetical sorting of treeview layers.

Use the gtk_tree_store_reorder method as it very quick.

This ordering can be performed on demand and works for any parent iterator (i.e. both sublayer and layer levels)

It should be called whenever an individual sublayer item is added or renamed (or after a group of sublayer items have been added).

Previously with insertion sort on every sublayer addition: adding 10,000 items would take over 30 seconds!
Now sorting after simply adding all tracks takes 1 second.
For a KML file with over 10,000 tracks (3Mb zipped) - See 'UK Hampshire Rights of Way'
 http://www3.hants.gov.uk/row/row-maps.htm
Enable Alphabetical sorting of layers within Aggregate layers

Primarily useful when one has only TrackWaypoint layers within a Aggregate layer.

Aggregrates maintain a list of layers which needs to be sorted as well as the treeview.
Enable TrackWaypoint sublayer alphabetical sort options.

These are saved in the layer properties for each sublayer types: tracks(including routes) and waypoints.

By default this is defaulted to off in order to preserve potential ordering of named items like:
10
100
1001

Otherwise the alphabetical sort will destory this order and otherwise ATM no other way to restore it.
[DOC] This internal setting no longer exists.
Remove now unused alphabetical sort functions as they have been superseded.
[DOC] fix ref doc
[QA] Use more explicit funcion name
Expose a function to iterate on all registered engines

Even if the function is trivial, it seems better to keep the list inside
the module and only offer a service to iterate (not offer the list)
Add a builder for a routing engine selector

User can give a function to filter the routing engines displayed in the
selector.
[QA] Add minor comment
[QA] Add type checking
[QA] More minor code improving
[QA] minor doc improvment
Generalize Acquire Directions

Since we have a generic routing framework, we can replace
Google Routing feature by a more generic solution.

The user is now able to select the engine for the route
computation.

Signed-off-by: Guilhem Bonnefille <guilhem.bonnefille@gmail.com>
Fix documentation minor typo
Merge branch 'LayerSort'
[DOC] Fix some incorrect docbook markup.