Display guidescan executable version in footer

[vineetbansal]

The guidescanpy web interface depends on installation of the guidescan executable (the guidescan-cli project) for many of its tasks (in fact it is not possible to run all tests successfully without it).

guidescan is installable from conda, typically by doing conda install -c conda-forge -c bioconda guidescan or by manual fetching of pre-built binaries from the guidescan-cli releases page.

It would be great to have the guidescan version information (by internally running guidescan --version) displayed in the web footer, along with the guidescanpy version there already. Of course this should accommodate the situation where guidescan is not available at all.

Some points to consider for a good implementation:

• The best place for this function would be wherever guidescan executable is currently used in the python code.
• The version number should not be determined every time any page is rendered, but just once, and then the cached value used subsequently.