[Crum/Flashcards] Organize the HTML

[pishoyg]

Assign IDs and classes more extensively. Use more appropriate tags.

[pishoyg]

This has an open TODO. We should implement it.

Other than that, the request is too vague, and it has no immediately visible benefit. So let's close it and revisit the HTML structure when a specific need for that arises.
Read about HTML best practices and apply them, then close when the status is satisfactory.

[pishoyg]

We would like to expand the Tidy config to the following:

add-meta-charset: yes
add-xml-decl: yes
break-before-br: yes
clean: yes
enclose-block-text: yes
enclose-text: yes
escape-cdata: yes
indent-cdata: yes
indent-spaces: 2
indent: yes
join-classes: yes
logical-emphasis: yes
priority-attributes: id,name,class
punctuation-wrap: yes
quiet: yes
sort-attributes: alpha
strict-tags-attributes: yes
tidy-mark: no
vertical-space: yes
wrap: 80
write-back: yes

NOTE: The Tidy config was set up as part of #213.
NOTE: We also thought of indent-attributes: yes, but we will likely abandon it.