[import VCF] Behavior if sample already exists in DB

[antonylebechec]

Describe the bug
By default, sample in VCF that already exists in DB is merge. That's particularly useful to import multiple VCF for one sample (such as VCF from multiple pipeline, SNV detection, CNV detection...).
On option should be also useful to change name of sample from the new VCF, in order to not merge but create a new sample in the DB. This can be useful for CQI samples, or for a sample name corresponding to different DNA extraction

Proposition: Autodetect existing names, push a warning box, possibility to change name of the sample in the "Samples" tab