Migrate COLOR constants to Color class & disallow implicit conversions to Color

[oxan]

What does this implement/fix?

• Migrate COLOR_BLACK and COLOR_WHITE constants to be static members of the Color class. Fixes error: 'BLACK' is not a member of 'esphome::Color' issues#2068.
• Disallow implicit conversions from an integer to the Color class. This conversion is rarely wanted, and has caused bugs in the past. This is (mostly) taken from PR Improve safety and correctness of color computations #1300.
• Mark the ESPColor alias in the light namespace as deprecated, as the docs already point out that it is.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other

Related issue or feature (if applicable): fixes

Pull request in esphome-docs with documentation (if applicable): esphome/esphome-docs#

Test Environment

• ESP32
• ESP8266

Example entry for config.yaml:

# Example config.yaml

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.

[probot-esphome]

Hey there @kbx81, mind taking a look at this pull request as its been labeled with an integration (ssd1331_base) you are listed as a codeowner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[OttoWinter]

LGTM 👍