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We move from awesome-typescript-loader (which is unmaintained) to
ts-loader and also upgrade webpack to be able to use the latest version
of ts-loader.
This new tool also emits declaration files for test files. We add
a tsconfig.build.json which ignores .spec.ts files and we make ts-loader
use this configuration file.

This adds three workflow related rql query creators.
They return a bound rql query (a tuple [query, vars]) directly usable
with transactionV2.
The result extraction is left to the user but is documented for each
query.
We could add a wrapper doing the query and extraction later but I don't
know which form it could take.

Closes #3.

If the schema is loaded, the load methods returns now an empty schema.

When making a GET request with the httpClient, the header
Content-Type: application-json was provided (which makes no sense).

[client, providers] Now import the schema from the server, with an integrity checking for optimisation

The method getFromCardinality was used instead of getToCardinality.
This used to work because there was no difference between the two previously ...

The cardinality information is read from a cardinality string, e.g. "?*".
There are two methods, getFromCardinality and getToCardinality to read the
cardinality for the subject and range/target, respectively, of the relation.
However the two methods were the same, both reading the first character.

In cardinality strings the first character correspond to the range/target of the
relation and the second to the subject/origin. Therefore, this changeset fixes
the getFromCardinality method to read its data from the second character of the
cardinality string.