Add None tile layer

Fixes #1472
More opacity options
Add preventDefault for click events (fixes #1771)
Add additional check to prevent snapping to area fills (fixes #1887)
Omit non-OSM features from search results (fixes #1890)
Add delete button to all forms, closes #1492
Removed the remove option from radio preset
Update translation
Fixes blank hover state for Structure field, closes #1891
Fixed radio placeholder assignment
Eliminate blank space in Structure hover state
Update D3 to 3.3.8
Moved localized delete button to the label, closes #1892
Simplify CSS and improve transition
Prevent 'zoom in to edit' from showing up during save success, closes #1792

Sets a background color, the same as the save state.
Better markup structure for background
Add a button to trigger file browser for GPX (fixes #1758)
Simplify CSS
Improve GPX related tooltips
Detect and dissuade stealing. Fixes #1896