Fix loading of nested attributes (Hashes) in REST adapter

[svoboda-jan]

This PR fixes loading of hashes from JSON. The previous way caused key-value attributes to be loaded as JS Object into opal, instead of Hash.

Also Model#from_form was updated to normalise hash keys and values:

'user[address]' => 'value'
#  becomes:
'user' => { 'address' => 'value' }

'user[]' => 'value'
# becomes:
'user' => [ 'value' ]

Another thing this PR fixes is Persistence#did_destroy, which weren't removing items from the RecordArray.

[svoboda-jan]

@adambeynon 👍 This PR is ready, but not sure what is happening with the CI.

[svoboda-jan]

@adambeynon Any update on this ? I have updated the PR and the CI seems ok now.

[svoboda-jan]

@adambeynon Any thoughts on this ?

[elia]

I'm going to close all PRs before archiving the project, due to lack of maintainers