#1467 Add mouseover Help for prices

[Ahasuerus]

Given the rising number of currencies that we support, we want to add mouseover help for currency values. It would be similar to the way we display mouseover help for publication formats. It wouldn't be as comprehensive as what FR 1158, "Allow multiple prices per publication", envisions, but it would be fairly easy to implement and it would be a step in the right direction.

[Ahasuerus]

Implemented in:

biblio/common.py
biblio/fc.py
biblio/pl.py
common/isfdb.py
common/library.py

Installed in SVN 827 on 2022-01-06. Closing the FR.

[Ahasuerus]

Part 2 - Added mouseover to the front page; moved the mouseover bubble to the left on Forthcoming Books pages:

biblio/fc.py
biblio/index.py
common/library.py

Installed in SVN 828 on 2022-01-06. Keeping the FR closed.