allow hard-coded port /foo to be changed via YARP_RENAME_foo

Adds support for a port renaming method of last resort. Suppose a program has a port called `/foo/bar` and there is no way provided to change the name of that port other than source code modification.  YARP already supports `YARP_PORT_PREFIX` which allows us to add a prefix to all ports.  Now, a port name can be changed entirely using `YARP_RENAME_foo_bar`.
For example:
```
YARP_RENAME_read=/logger yarp read /read
```
will open a port named "`/logger`" for shells where this syntax is permitted.  Renames (if present) are applied before prefixes (if present).