Improve fields and field types definition in SolrSchema

Primitive fields and field types currently defined in the schema should be analysed/revisited in order to 

• make clear their purpose and the scenario where they are involved in
• make sure (field types only) they are using the most appropriate Solr type according with that purpose (e.g. Trie types have been deprecated in favour of Point fields)
• make sure the options/flags set on each field/field type provides the best configuration according with its purpose (e.g. indexed/stored/docValues)

Potential expected benefits we are looking for as consequence of that refactor: 

• disk space usage (e.g. if a field is single valued and it is docValues enabled, we could avoid to store it)
• better memory usage (e.g. use docValues for sort / facet fields)

At first sight it seems there is some space of improvement. See for example the following field definition: 

<dynamicField name="int@sd@*" type="int" stored="true" docValues="true" />
<dynamicField name="long@sd@*" type="long" stored="true" docValues="true" />
<dynamicField name="float@sd@*" type="float" stored="true" docValues="true" />
<dynamicField name="double@sd@*" type="double" stored="true" docValues="true" />
<dynamicField name="date@sd@*" type="date" stored="true" docValues="true" />
<dynamicField name="datetime@sd@*" type="date" stored="true" docValues="true" />
<dynamicField name="boolean@sd@*" type="identifier" stored="true" docValues="true" />
<dynamicField name="category@sd@*" type="identifier" stored="true" docValues="true" />
<dynamicField name="noderef@sd@*" type="identifier" stored="true" docValues="true" />

where as you can see both stored and docValues options have been enabled on single valued fields. 

Acceptance Criteria

• This doesn't include fields (mainly text fields) already managed in SEARCH-2068
• There are useful comments in the schema about the usage and the purpose of each field/field type
• Primitive Fields / field types are properly configured according with their purpose/usage 
• No regression