This makes sure that validation uses the correct values.
Otherwise the validation of checkbuttons may overwrite the values
of depending entries.

 - move necessary validation functions into Settings.pm
 - check against FIJI ports too

 - validate nets and respective drivers like everything else
 - load the netlist earlier (in the user scripts) to make it available while
   loading settings
 - add a FIJI::Netlist parameter to respective FIJI::Settings's functions
 - add a new type 'driver' for FIU elements to distinguish its string
   representation from nets'
 - add new net validation function to FIJI::Netlist
 - use this to make net and FIU validation more generic to simplify FIJISettingsViewer
 - refine and correct handling of the tool phases
 - distinguish fatal errors, missing fields and less important anomalies when
   validating settings depending on the phase etc
 - notify user about validation problems in more detailed messages and tooltips
 - refine FIJI::VHDL to not load settings all the time and receive parameters
   directly instead of via hashes
 - use a global constant ONLY_LOAD in fiji_setup instead of a local variable
 - add a 'show_warning' function to ease opening warning dialogs
 - various other usability/GUI-related improvements
 - allow the deletion of nets

as expected

Moved rebinding to function in Tk::FIJIUtils, added calls to
this function for every entry.

Addresses issue vecs/fiji#63 discovered in usability test

Addresses issue vecs/fiji#39

Addresses issue vecs/fiji#54

However, allow the user to disable these popups for the current session.

 - extract _add_driver_radiobutton_list from existing code
 - refactor it to allow it to be called repeatedly while reusing widgets
 - make some private Netlist functions public as they are used elsewhere :/
 - eliminate duplicated nets (low-hanging workaround) for a nuisance
   of _get_net_connections().
 - add FIJISearchWidget to the dialog and call _add_driver_radiobutton_list
   from its callback after filtering the driver list

Make the entry + search button + substring/globbing/regex choices
reusable as standalone widget.

Use the previous regex to validate the name only and check for a
defined non-empty string when using the names to append to indexed
names like "FIU 42".

Fix vecs/fiji#60 eventually.

Related to vecs/fiji#60

Related to vecs/fiji#60

(use_vars is default anyway thus drop it)

fixed invalid comparison and unnecessary print

Log it as an error but do not report it as such to certain callbacks thus
allowing to still save a replay configuration after an abort.