removed redundant getDefaultSchema in mysql5 module - this is already defined in base dialect
modified getDefaultSchema() to return the username in uppercase

afaik the default schema of a user is always the username in uppercase (at least by default)
simplified wrapping of connection methods
modified tableExists: lowercase table names before check to avoid differences in case sensitivity between mysql/oracle/h2

this change is necessary because mysql on windows is case insensitive, so models with an upper case table name
result in a lowercase table in db. without lowercasing sqlstore would try to create the table again which ends
in an exception.