Added support for ICS COLOR property (#188)

[Aga-C]

What is it?

• Bugfix
• Feature
• Codebase improvement

Description of the changes in your PR

• Added support for importing and exporting COLOR property.
• Because COLOR uses a color palette (according to RFC 7986), I've added an extra property X-FOSSIFY-EVENT-COLOR to store the exact color.
• If a color isn't from the predefined palette, the closest color is chosen (found as a color with minimal Euclidean distance).
• X-FOSSIFY-EVENT-COLOR is stored directly after COLOR, so it will always overwrite approximated color from COLOR.
• COLOR is not exported if event color is the same as event type color.

Fixes the following issue(s)

• Fixes Implementing color-data to ICS import / export for events (part of RFC 7986) #188

Acknowledgement

• I read the contribution guidelines.

[naveensingh]

Just made some code style changes, everything works and looks good!

The getDisplayColorFromColor() function should probably be removed or should only be used in UI because currently we are exporting modified event colors.

Thanks!