Allow for deletion of selected text

Allow for deletion of selected text on Ctrl-B.

Before my fix:
Situation 1: Address bar not selected. Ctrl-B deletes current address and goes to URL.
Situation 2: Address bar selected. Ctrl-B adds clipboard data to the end of selection.

After my fix:
Situation 1: not changed
Situation 2: Delete selected text (partial or all) from address bar, then copy the clipboard data.Allow for deletion of selected text on Ctrl-B.

Before my fix:
Situation 1: Address bar not selected. Ctrl-B deletes current address and goes to URL.
Situation 2: Address bar selected. Ctrl-B adds clipboard data to the end of selection.

After my fix:
Situation 1: not changed
Situation 2: Delete selected text (partial or all) from address bar, then copy the clipboard data.

Can probably be programmed more elegantly but it works.
Update main.js
Merge pull request #4 from CaspianRoach/patch-1

Allow for deletion of selected text