Support for MsSql dialect in RawStatisticsRepository implementation

As discussed in #181

Now supports global property:
`# The SQL dialect used at the backend of JDBC connection. defaults to mysql`
`oxalis.jdbc.dialect=mssql`

When the property is set to `mssql`, `RawStatisticsRepositoryMsSqlImpl` will be loaded.
If the property is set to `mysql`, or the property doesn't exist, `RawStatisticsRepositoryMySqlImpl` will be used. If the property value is set to any value except `mysql`or `mssql` an exception is thrown.

With the following settings in oxalis-global.properties I successfully Oxalis statistics against an Microsoft Azure MSSQL server:
`oxalis.jdbc.driver.class=com.microsoft.sqlserver.jdbc.SQLServerDriver`
`oxalis.jdbc.class.path=file:///home/shared/mssql-connector-jdbc/sqljdbc4.jar`
`oxalis.jdbc.dialect=mssql`
`oxalis.jdbc.connection.uri=jdbc:sqlserver://dbservername001.database.windows.net:1433;databaseName=SomeDataBase`
`oxalis.jdbc.user=someusername@dbservername001`
`oxalis.jdbc.password=*******************`

Note: In the Github merge view, the changes made seems larger than actually done. Many lines that isn't really changed, is marked as -, then later as +. I guess the merge view isn't as good as the one from TortoiseGIT.

Anyhow, the **current behavior of Oxalis statistics modules has not changed**, unless one changes oxalis-global.properties..