[web] Create ColorSelectorButtons in ColorSelector iteratively to reduce repetition

Summary:
Instead of copy/pasting this 10 times, we can easily create ColorSelectorButtons iteratively thanks to the flex-wrap layout.

Depends on D3703

Test Plan:
Things continue to look/behave as expected:

Reviewers: palys-swm, def-au1t

Reviewed By: palys-swm

Subscribers: ashoat, Adrian, karol-bisztyga, benschac, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3704