Include shared blocks in appOptions.level

[balderdash]

Pass block pool blocks to the client as appOptions.level.sharedBlocks. These blocks include a bit more information than the existing custom blocks, structured as so:

sharedBlocks: [
  {
    name: 'block_name',
    category: 'Toolbox Category',
    config: {
      <custom block config>
    },
    helperCode: 'function someHelperFunction() {}',
  },
  ...
]

The custom block config is the same as the existing level-specific custom block config, documented here.

After installing the blocks, append them to the specified categories unless level.hideCustomBlocks is set.

[balderdash]

Ability to add LB-created blocks to a shared “block pool”

[joshlory]

Code changes LGTM. What is the plan to test this feature?

[balderdash]

I'll add some unit tests in a followup PR to check that appOptions.level.sharedBlocks is being populated as expected, but I'll need a UI test to verify that blocks make it all the way from the DB to the blockSpace.