Class name caching should be case-insensitive

[jbilcke]

Hi,

The OrientDB server considers that class names are case insensitive, but not OrientJS.

It looks like OrientJS stores the first version of the class name it sees as-is (eg. capitalized), which prevents applications expecting the same case-insensitive behavior than OrientDB from querying the data (eg. using a lowercased class name).

The problem seems to be related to these lines:
https://github.com/orientechnologies/orientjs/blob/master/lib/db/class/index.js#L289
https://github.com/orientechnologies/orientjs/blob/master/lib/db/class/index.js#L296
https://github.com/orientechnologies/orientjs/blob/master/lib/db/class/index.js#L327