Add gender identity and expression

[KathleenLD]

This PR adds gender identity and expression to the Berlin Code of Conduct. Gender identity and gender are not the same thing, and I hope this change can help Berlin conferences and user groups be a little more trans inclusive.

cc @kkaefer @PragTob

[myabc]

@KathleenLD you might want to take a look at #63, as this PR bears some similarities.

[varjmes]

Hi there, any word on either of those PRs? This CoC is a great start but I don't see it to be trans inclusive at this time, meaning I wouldn't feel particularly welcome.

[lauralindal]

Hi @varjmes and @KathleenLD - we're finally back on working this out. Do you think that "gender identity and gender expression" is an appropriate/trans inclusive wording? I would vote for merging this PR, then :)

[aldavigdis]

Hi @lauralindal, @varjmes and @KathleenLD. Gender identity and gender expression is perfectly suitable and inclusive IMO. (Anything additional like respect for pronouns etc. can be interpreted from this, so I don't think it's needed to mention it specifically.)

Also, I stumbled across this PR as I was looking into adapting the Code of Conduct for some LGBT-related activities, so it would be nice to see this PR merged soon.

[lauralindal]

thank you, @aldavigdis !
@skade can we please mearge this :) ?