Allow files to be tagged as interesting

Interesting files contain things that seem likely to produce false
positives -- that is, an unusual sound that uses the call frequencies.
If an interesting file is an extract of a larger file (e.g. one minute
from a 15 minute recording), it could be productive to look further at
the rest of the interesting file.

This is quite a hack in terms of the database.
Use sound position when drawing playing line, not dead reckoning

Before the line would be advanced a pixel at a time at a supposedly
regular interval without reference to the sound position, which appeared
to work well over short stretches, but could lose its place by a second or
so over several minutes.

Now we ask the audio where it is, and work from there. To keep things
moderately smooth, we need to check more often.
Fiddle again with spectrogram colours: less yellow, more contrast

Blue polynomial is a bit crazy.
gitignore results files
Server: add a facility to ignore some wave directories

Sometimes you just want to concentrate on one source.
keep track of the number of interesting files
fiddle with the spectrogram polynomials AGAIN.

I can't help it.
Rework the interface using control-drags for resizing, & showing draggee

This makes the longer calls easier to do, perhaps to the detriment of
finetuning.

The "M" key now merges overlapping calls of the same colour.

There are fewer ghost artifacts, and the call being manipulated is now
shown as it changes.
"O" key turns all calls off

This is often what you want.
Add keyboard shortcuts for marking as interesting and saving
fiddle again with spectrogram, and shuffle messages at top of screen