Updated the default mapping of Int64 to NUMBER(19,0) to match the default type mapping used by Oracle.

See Table 3-4: Mapping of Oracle Data Types and EDM Types (http://docs.oracle.com/cd/E11882_01/win.112/e18754/featLINQ.htm)
Merge pull request #349 of kramerpr/master

  Updated the default mapping of Int64 to NUMBER(19,0) to match the default type mapping used by Oracle.