[Plug-Extension] Add Cancel button to Remove Account Modal (Improvement )

[alinasytnik]

Plug Extension - Improvement - Remove Account Modal

Steps to Reproduce
1 - Open Plug Extension and go to Profile menu
2 - Import an Account from Import Wallet menu
3- On Profile side drawer notice the imported account when user hover on it, it has a red circle icon
4 - click on it and Remove Account Modal is displayed
5 - Notice no Cancel button is present.

Actual Result

Expected Result
Add Cancel button to be in compliance with other modals