Trying to make sense of classificationUtils.registrationEmail()

* Extract dateFormatting
* Move variables closer to where they are used
* Use classification.registrationDate instead of now if it exists (doesn't exist in web preview)
registrationEmail: Fix previousClassification returning nonsense.

Every reclassification email actually contained the current classifications data as the previous classification data.

There are actually 3 distinct cases here:
1) Web preview: new	classification is in drafts, previous on is program.classifications[0] if it exists
2) Upon registration: new classification is program.classifications[0], previous is program.classifications[1] if it exists
3) rootEditMode web preview: "current" classification is somewhere in the array, previous one is program.classifications[n+1] if it exists
Fix email content when previous classification has no registrationDate

Used to be "Kuvaohjelmaluokittelija oli NaN.NaN.NaN arvioinut kuvaohjelman"

There are ~5000 of these...
Fix email content when previous classification only has legacyAgeLimit

Used to be "... kuvaohjelman ikärajaksi 16 ja haitallisuuskriteeriksi ."

There are ~120000 of these.
Refactor classificationUtils.registrationEmail()

* Move all functions not used elsewhere into registrationEmail()
* Extract functions to keep some separation of concerns
* Keep the beef at the top, details below
email: public comments are no longer required
Now that it's a bit less buggy, let's add images to the email

* Add logo image on top
* Show current classification agelimit and warnings as images
Fix: need to parse registrationDate if it exists
Fix email preview in rootEditMode for old classifications that don't have criteria.
Fix dialogs

* Vertical centering with display:flex.
* Make them all look the same -> border, autoWidth, textaligns etc.
* Remove obsolete .remove-user-dialog from templates.
* reset-password page had practically nothing to do with .dialog class, so cleaning it out. Also, the html was quite interestingly laid out.