Make beacon search specific, remove reference selection

[talavis]

Describe the pull request:

• Bug fix
• Functional change
• New feature
• Code cleanup
• Build system change
• Documentation change
• Language translation

Pull request long description:

The earlier version used the wrong datasetID for searches. The Beacon system currently interprets incorrect datasetIDs as "search in all datasets", ie the old search checked all datasets. An example
is 4-100118858-C-T - earlier both ACpop and SweGen reported it as present, now it is (correctly) absent in ACpop.

The reference selection is also removed from the frontend. It would always contain only one choice (the reference used by the dataset), and led to a <select> element with only one value available.

Finally, a "show example" text has been added, which fills the form with the variant 22-46615880-T-C, which is also used in the browser.

Changes made:

• The datasetID is now taken from Beacon, allowing correct searches.
• Reference selection is removed from the frontend.
• "Show example" "button" added.