Multiple reprojections lose original vertices

[sindizzy]

Reprojects all layers in the map frame so that they use new projection. Before they are reprojected the layers will get reloaded from the original source if available. This is useful when doing multiple reprojections on a layer as the reprojection will occur on the original vertices and not the reprojected vertices. For certain workflows multiple reprojections will tend to lose the original vertices and result in unexpected coordinates. This method attempts to alleviate the issue. This method also includes drawing layers, although they may lose their original vertices since they don't have a source from where we can reload.

Fixes #1104 and #782.

Checklist

• I have included examples or tests
• I have updated the change log
• I am listed in the CONTRIBUTORS file
• I have cleaned up the commit history (use rebase and squash)

Changes proposed in this pull request:

• Before reprojection of a layer it is reloaded from the source (if available) so that the original vertices are always used as the main source.
• This method also includes drawing layers, although they may lose their original vertices since they don't have a source from where we can reload.

[sindizzy]

This PR will be closed in lieu of the refactored PR here #1470