rewrite modules to merge similar species

[westram]

There are 2 modules attempting to do that job:

• join species (old)
• merge similar species ("new")

Goals:

• remove old module
• improve new module:
  • allow to define what shall happen if (2 or more) merged species have different content in one field.
    • possible actions (for all fields):
      • abort with error
      • use "first" (aka randomly choose one species as source)
      • remove these fields
      • move contents into a new string field (e.g. "nuc" (GB_INT) → "nuc_merged" (GB_STRING)) and then apply merging as done for GB_STRING fields
    • possibilities for GB_STRING
      • concatenate fields (either separate by some character, e.g. '#' or use "[TAGS]")
  • allow to delete source species after successful merge

---

related: #59, #61