Feature: Overhaul of the Vertex tool

The Node tool (now renamed to Vertex tool) has undergone a complete rework to make it more flexible.
Some of the more important changes are:

1. Instead of requiring users to first select a feature and then edit its vertices in the second step, the tool now capable of working with multiple features at the same time. It is therefore easy to select vertices from several features and move or delete them at once. If there is a need to constrain selection of vertices to just specific feature(s), it is possible to select the features with selection tool first - the vertex tool will only work with vertices from selected feature(s) in such cases.
2. Instead of working just with the currently selected layer, the tool is now able to work with all layers that are in editing mode at the same time. Moving of features that logically belong together but are located in different layers has got much easier. Still, the current layer is respected if there are multiple choices when picking vertices.
3. Features and their vertices get highlighted as the user moves the mouse pointer over them, giving better visual feedback.
4. In QGIS 2.x the vertices would be moved by clicking a vertex, dragging it with the left mouse button still pressed and finally dropping them by releasing the mouse button. This behavior has been changed to "click-click" approach where user first clicks a vertex to pick it, then drag it without having any mouse buttons pressed and drop it by clicking again on the final destination. The arguments for this change were the following:
5. it is easier to precisely place nodes (not having to apply force to the mouse button all the time)
6. one does not move nodes inadvertently
7. it is possible to cancel the operation
8. it allows to pan the map by pressing space bar while the node is being moved

See https://github.com/qgis/QGIS-Enhancement-Proposals/issues/69 for more information.

This feature was funded by QWAT

This feature was developed by Martin Dobias (Lutra Consulting)