[Cashtab] Reduce bundle size by 70kb (10%)

Summary:
Replace import of full lodash module with individual functions.

This reduces the size of the gzip JS bundle from 726kb to 642kb.

Test Plan:

docker build -t cashtab_local .
docker run --rm -p 8080:80 --name cashtab cashtab_local

Navigate to localhost:8080 and check the size of the largest bundle in the Network tab

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9481