[Cashtab] Better looking notifications

Summary:
T1765 T1763

• Add eCash logo for sent/received xec tx notifications
• Add eToken logo for sent/received eToken tx notifications
• Standardize notification style

Test Plan:
npm start
For all of the below, make sure the notification doesn't look busted:
Receive an xec tx
Send an xec tx
Receive an eToken tx
Send an eToken tx
Create a token

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9914