Lots of bugs fixed in PhenoLoader
1) Fixed crash if no metadata is added in PhenoLoader
2) More graceful behavior when Phenoloader cannot parse filenames: Implemented a
try-catch and an error dialog is now thrown with suggestions. Got rid of
various temporary fixes that let the user get past the marker page and could
have resulted in unpredictable subset of files being selected.
3) Better filename extension detection in PhenoLoader: Files without extensions are marked as
such and no longer cause crashes.  We now use the same recursive directory lister
as the rest of PhenoRipper. This prevents files without extensions being
identified as directories. Use strcmp instead of regexp to demand
perfect matching (tiff and tif are now different).
4) Fixed crash on PhenoLoader metadata fields being given names
that are not valid matlab variables (these are modified
by passing through genvarname now)
5) More reliable and consistent detection of multichannel files in PhenoLoader:
Use the same method as the engine. We actually open the images now and don't rely on tags.
Also fixed false assumption that multichannel files must have 3 channels.
6) Fixed wierd behavior with multichannel files in PhenoLoader: Got rid of handles.nBImages and
initialized handles.multichannel right at the start of PhenoLoader.
7) Added Image as name of filename display column in PhenoLoader when
showing metadata for multichannel files: This was previously empty but
showed Image:# for single channel files.
8) In the PhenoLoader marker page focus now starts with the names of markers
for multichannel file, rather than of the filelist since the channels are
automatically detected in this case.
9) In the PhenoRipper Wizard Metadata, fixed crash on pressing cancel when loading from metadata file