[Cashtab] Airdrop Option - ignore own address

Summary: Option to exclude the airdrop sender's address from the list of recipients.

Test Plan:
npm start
ensure normal airdrop calculation is correct
tick the Ignore my own address option then ensure airdrop calculation excludes the active address, including the distribution ratio of XEC

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D11245