Enable donate to multiple projects in single call

[lachlanglen]

Title

Add batch donation in single call

Summary

Currently calls to donate are batched, which has limits (e.g. Meteor Wallet doesn't batch more than 8 transactions together) and also uses more gas than would be used to donate to multiple projects in a single method call.

Motivation

[More detailed explanation of the motivation for the enhancement, including any benefits it would provide]

Description

Considerations include whether to adapt existing method or create separate method for batch donating.

Alternatives

[Discussion of any alternative solutions that were considered and why the proposed solution is preferred]

Risks

[Identification and mitigation of any potential risks associated with the enhancement]

Acceptance Criteria

[List of criteria that must be met for the enhancement to be considered accepted]

Additional Information

[Any other relevant information, such as links to related issues or pull requests]