Add description as caption in lightgallery dialog and below image

[faustefan]

Hi Gauthier,

as discussed via mail, please find enclosed the suggested changes:

• to remove the ! from description text
• to show description as caption in lightgallery - enabled by default
• to show description as inline-caption below the image - disabled by default

Please let me know if further adjustments are needed or if you are facing any problems during testing. I have tested against my own documentation project using mkdocs & mkdocs-material theme successfully.

Best regards, Stefan

[g-provost]

Thanks for your help improving the extension.