Support DSM 6 and 7

Support DSM 6 and 7

Small changes for DSM 6:

All fields (except enable_syno_token as explained below) must either be in the GET params or the POST params, you can't mix GET and POST params
enable_syno_token=yes must be in both the GET and POST params.
If enable_syno_token=yes is only in the POST fields, then DSM6 returns a synotoken of --------. If enable_syno_token=yes is only in the GET params, then it returns no synotoken at all. It must be in both to work.
Need to use /webapi/auth.cgi instead of /webapi/entry.cgi
Verified with DSM 6.2.3-25426 Update 2 and DSM 7.0-40850