Metacat

Worked around to remove all hard-coded release number on the code. Now the documentation will read the Metacat release number from the metacat.properties file and we don't need to manually edit the release number anymore.

Remove some hard-coded link on the release number. But there are still have four ones on the http link.

With the help of Roger, the release will read the version from the metacat.properties file rather hard-coded.

Use the variable release to replace the hard-coded version.

Use the variable release to replace the hard-coded version. The release variable can be modified on the conf.py file.

Use the |today| which will be auto generated the current date to replace the hard code of the release date.

Change the version and release to 2.8.0.
Add a date format property.

Change the newest version to 2.8.0

Change the version to 2.8.0

Merge changes from the 2.6.0 release.