Updates to proposed LGBTQIA+ flag designs

[mattcen]

• Update colours of Bi+ flag to match colour codes at https://en.wikipedia.org/wiki/Bisexual_pride_flag#Design_and_colors
• Add Pansexual flag using colours from https://en.wikipedia.org/wiki/LGBT_symbols#/media/File:Pansexuality_Pride_Flag.svg
• Rename Trans PNG to match name of its related SVG
• Update Trans SVG to show borders where two white circles intersect

[KathyReid]

These changes look FANTASTIC, thank you so much @mattcen. I'm going to merge them into the branch, which means they should be available for others to review as well.

[mattcen]

These changes look FANTASTIC, thank you so much @mattcen. I'm going to merge them into the branch, which means they should be available for others to review as well.

Thanks @KathyReid! I was too slow, but I did eventually work out how to reduce the diff of the Trans flag (I was being too clever). It's at https://github.com/mattcen/brand-guidelines/commit/9da502389ae3f69390fa66dbad8bfcdea025858b if you want to squash the fixup onto the top commit of #4 for tidiness.

Here's how it looks: https://github.com/mattcen/brand-guidelines/compare/lgbtq-variations~2...mattcen:lgbtq-variations?short_path=83ce13d#diff-2469e14bd9ebaa268f258f879f014ee9