Add import validation dialog

[subdavis]

@BryonLewis not ready for code review yet, but if you could give some general feedback about how this tracks against what you had in mind, that'd be appreciated. Is this going in the right direction?

fixes #606
fixes #622

Relevant to parts of #417 as well.

[BryonLewis]

Yeah this is definitely going in the right direction. I'm a little afraid of the complexity that might be added with the other import issues/tasks in our backlog but this is great.

Going to apologize for this brain dump of questions/comments:

• Is the idea to use the same dialog as a platform for [FEATURE] Desktop: add ability to open image files based on glob selector #622 and [FEATURE] Trans-code videos and run-pipelines in one stage (or just same time) instead of two #530?
  • If so we may want place some of the extra details in a 'details' expandable area to reduce a bit of the clutter of "importing transcoded image sequence with a glob pattern that you want to run an immediate pipeline on". I think you see where I was getting afraid of the complexity. I don't know what to do for this instance while still making it simple for others. I have some minor ideas but everything seems to add complexity.
• 'Continue to ignore warning' might not be descriptive enough. There is some ambiguity if ignore means overwriting or adding an additional dataset (Although it is indicated as a newID). Especially if only one other dataset with that name/source is found.
• Dataset Name @ ID might be better swapped to Dataset Name @ Imported date if we save the creation date? I don't think anyone besides us cares about unique IDs. Could possibly add an import date and a modified date.
• Quick peek at the code looks like you give them option to name a dataset even if there aren't duplicates 👍

[subdavis]

Ready for review. Your comments were good, I made all those changes.

[BryonLewis]

I really like this for the import tool. It makes a lot of sense and gives a good point for some of the other tasks.

Just some things involving edge cases and trying to improperly import data.