Complete Studio's doc

[santo-it]

There are some sections or subsections with no text e.g.:

• http://orientdb.com/docs/master/Graph-Editor.html
• http://orientdb.com/docs/master/Edit-Vertex.html
• http://orientdb.com/docs/master/Edit-Document.html

It's important we review, complete and improve the Studio documentation as users experience is quite linked with Studio

[santo-it]

To update also http://orientdb.com/docs/master/Studio-Schema.html (now that https://github.com/orientechnologies/orientdb-studio/issues/21 and https://github.com/orientechnologies/orientdb-studio/issues/431 have been implemented)

[santo-it]

To document also the graph editor configuration limitation for the root user, as described in https://github.com/orientechnologies/orientdb-studio/issues/254