User defined configuration files currently are supported for local
directory (.) and `basler` subdirectory. However, other GenICam cameras
can be used with this IOC. Therefore, make the `genicam` folder also a
possibility to supersede the previous `basler` directory. The
specification of the `basler` directory is kept for backward
compatibility with existing deploys.

Defining the autosave in device.cmd makes the current template
configuration not possible to be changed by users without conflict. This
would render users to drop device.cmd entirely. Thus, move the call to
autosave template in the st.cmd template. This also makes the template
script more clear about the usage of autosave.

This makes possible to remove the hardcoded path used in the shebang,
aiming at removing all the startup iocsh template script dependencies
of the build directory.

A post-install phase is used to create symbolic links instead of
changing the INSTALL_LOCATION. This change is backward compatible, as
the binary can still be found in the previous path.

Templates loaded with relative path requires that we `cd` to the
template directory at the start of the iocsh script. This makes it
harder to define autosave requirement files to be loaded based on the
user's current directory, which is desired when it is mounted as a
volume.

Avoid changing the directory entirely by using absolute path for IOC
configuration files based on `envPaths` definition. This makes it clearer
which loaded files are templates and which are locally defined.

Note that this configuration makes it the entire script independent of
the build and install location of the IOC, since `envPaths` is placed in
a standard directory. It has been chosen to be under `share/misc` as it
is a single application architecture-independent configuration file [1].

[1]: https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch04s11.html#usrsharemiscMiscellaneousArchitecture