Merge pull request #125 from yosiat/master

Fixing previous commit while improving performance
Fix #118 change inaccurate location marker opacity to 0.5
Fix #121 change date filter ranges to whole last 4 years

For anything else, the user should use the 'choose date' option.
Fix #107 display small accident icons in sidebar
Fix #116 clicking on severity filter checkbox text will also change it
Merging