Update menu dropdown styles

- Replaces thick shadow on dropdown menus with a fuzzy shadow.

- adds more padding between dropdown menu items

- adds a pointer cursor to indicate the items are clickable.

To view the changes check out the branch, then click on "Add build step" on the configure page for any job.

<img src="https://camo.githubusercontent.com/434bb476797908b20b7fe186daba44448fb14b32/68747470733a2f2f6170692e6d6f6e6f736e61702e636f6d2f696d6167652f646f776e6c6f61643f69643d45354447764f774e75616c77743547654a53663035527338316e4f6d4635" />