Remove orphaned mantidplodi.dic file in SINQ directory

Refs #7505
Move LoadFlexiNexus to DataHandling\\Nexus category

Refs #7505
Move Poldi algorithms to SINQ/Poldi category. Refs #7505
Remove unrequired cpp files in SINQ/test. They will auto generated.

Refs #7505
Add copyright to headers that don't have it.

Refs #7505
Merge branch 'feature/7505_sinq_code_check' into develop