Update data retrieval style and dataset selection

Data preview (table view) now overflows the container.
Makes it clearer to users that there are more columns.
Rename Choice 1/2 to Select, not perfect.. but better, it takes less
space
Disable/enable weather/event selectors

The selectors will be enabled or disabled when a station is selected.
Request from API if selected station has weather/event data.
Update API url processing, prevent multiple trailing slashes.