Layer and map page updates

- Applying validation to layer and map name to ensure that there are no duplicates.
- Updates to modal windows including that the backdrop has now been set so that the user cannot dismiss the window without using the buttons.
- Adding to the layer page so that a layer must be selected prior to adding it to a map.
- Adding real data to map dropdown, ensuring that the map section doesn't appear until at least one layer is selected.
- Adding Add to Map button and save message.
- Altering dropdown style to bootstrap.
- Fixing download popup menu to sit on top of all other elements and follow window scrolling.