Add button widgets

Summary:

• Don't use deprecated router-link's tag property
• Make the code more concise
• Make the output files smaller

Test Plan: ./phpunit --testsuite=Browser

Reviewers: #hkccp_developers, mollekopf

Reviewed By: #hkccp_developers, mollekopf

Subscribers: #hkccp_developers

Differential Revision: https://git.kolab.org/D3373