Pycatsearch

- The search is now instant. There is no need to click the _Show_ button.
- The substance choice can be more precise via double-clicking a line in the list of the substances. If there is more than one substance behind the line, an additional dialog appears.
- When the filter of the substances' list is empty, the checked items are at the top.
- There is no search timeout anymore, for the search is fairly quick anyway.

Fixed:
- a crash when saving a downloaded catalog,
- the Substance Info dialog shown only once for a substance in the list,
- the Preferences dialog geometry not saved,
- search by ID didn't work.

Added:
- a link to the CDMS web portal in the Substance Info dialog (see the ID),
- customizable URL templates to browse substances by InChI key from the Substance Info dialog,
- search by InChI key.

Changed command-line options related to the search by InChI key.

It's getting harder to ensure compatibility with old Python versions day by day. This time, the app crashed without a traceback on copying.

Fixed wrong units appended to the values when copying/exporting the data with units.

Added movable parts of the interface to easily tune the window to everyone's needs. Now, the table of the results and the two upper sections can be resized, and the columns of the table can be in any order.

Urgent release to fix file dialogs not showing up.

Less important changes:
- fixed that ugly 99% progress at the end of downloading catalog data,
- refactored Preferences dialog to make it smaller,
- added icons from [`qtawesome`](https://github.com/spyder-ide/qtawesome) if it's installed,
- added an option to ignore a new version and not to warn about it.

Added _Check for Updates_ action in _Help_. With some luck, this will check for updates and install them if ones found.