[RFR] Add project configuration to API model

- [x] Add configuration item
- [x] Add previous analyses hashes
such tags with dots in them look weird to me, and absolutely not XMLish.

Maybe this should be exposed in a structure looking more like what Symfony does in its XML config files for prototyped array nodes:

```xml
<rule name="composer.apc_class_loader_should_be_enabled">
  <enabled><![CDATA[0]]></enabled>
</rule>
<rule name="php.class_too_long">
  <max_length>500</max_length>
  <threshold>5</threshold>
</rule>
```

An advantage is that it would be much easier to traverse the XML with XPath than when having dynamic tag names based on the rule name (relevant for people consuming the API without the SDK)


and then the following might be more readable (but a bit inconsistent with the way the Insight XML looks like currently):

```xml
<rule name="composer.apc_class_loader_should_be_enabled" enabled="true" />
```

But the possibility to do such changes actually depends on how much BC you need on this part of the API (I don't know when it was deployed).
what do you think about this @lyrixx ?