GUACAMOLE-422: Use TIMEZONE rather than TEXT fields for RDP/SSH "timezone" parameter.

It has been confirmed that the TIMEZONE field does indeed represent IANA
time zone database IDs, as required by the "timezone" parameter.

guacamole-ext/src/main/resources/org/apache/guacamole/protocols/rdp.json

@@ -108,7 +108,7 @@
                 },
                 {
                     "name"  : "timezone",
-                    "type"  : "TEXT"
+                    "type"  : "TIMEZONE"
                 },
                 {
                     "name"    : "console",

guacamole-ext/src/main/resources/org/apache/guacamole/protocols/ssh.json

@@ -80,7 +80,7 @@
                 },
                 {
                     "name"  : "timezone",
-                    "type"  : "TEXT"
+                    "type"  : "TIMEZONE"
                 },
                 {
                     "name"  : "server-alive-interval",