Summary:
Added support for `createPaste` in Sandy plugins
Nice minimalistic example of how to expose a Flipper api to Sandy.
Note that some indirection could be removed by having an interface that is shared directly between `BasePluginClient` and `FlipperLib` (e.g. `PublicFlipperLib`). In contrast to `addMenuEntries` from the previous diff, `createPaste` is basically exposed verbatim to Sandy without additional wrapping, so those cases could be made simpler. Maybe will do that later.
Reviewed By: passy
Differential Revision: D22815873
fbshipit-source-id: e6d0773a35341edfe5de0898317eaadf88de79d0
7c6065889d