Terminal: HyperLink: Remove base address, add text property

* The base address is no longer used (it was in a an earlier, never
  committed version), so we can as remove it.
* Introduce a text property.
Terminal: hyper link mode: handle relative paths better

* We were trying relative paths as is, which means checking them with
  Terminal's current working directory. Now we use the CWD of the active
  process.
* In case the path is relative, add a context menu item "Copy absolute
  path".
Terminal: hyper link mode: Try more aggressively to detect a path

Consider ':' a potential path delimiter and try all combinations of
chopped off prefixes and suffixes. This makes detection in the output
of a multi-file grep work even if the found line starts with a path
character or is a path. A path in the typical colon delimited search
paths (e.g. PATH) is detected as well.