Feature/r2.6.0 doc updates

Changes staged at:
http://stg-web101.sw.joyent.continuuity.net/cdap/2.6.0-SNAPSHOT/en/developers-manual/index.html

- Fixes https://issues.cask.co/browse/CDAP-728 ; see
 http://stg-web101.sw.joyent.continuuity.net/cdap/2.6.0-SNAPSHOT/en/developers-manual/building-blocks/services.html#about-path-parameters
The reason for the change was because the commands (lines 102 & 103) used "element" and this was a simple change to be consistent with that. If we don't do this change, we should change line 102 & 103. But I don't really like "program-type" for a flow, as I don't think of a flow as a program. Is there something else we can use?