Make boilerplate maker/loader functions

[hzovaro]

As per title.

• [x] Make a new submodule called io or something
• [x] Replace load_<survey>_df() with a generic load_df() function
• [x] Do the same for load_<survey>_metadata_df()
• [x] Replace make_<survey>_df() with a generic make_df() function that calls _process_gals from the survey-specific files
  • [x] SAMI
  • [x] Hector
  • [x] S7
  • [x] LZIFU
• [x] Update example scripts, etc.
  • [x] SAMI
  • [x] Hector
  • [x] S7
  • [x] LZIFU
• [x] Create a new wiki entry with instructions on how to incorporate a new survey
• [ ] Make it so that users can pass in the name of a local module and/or functions instead of having to put their file in the io directory?
• [x] Replace _2d_map_to_1d_list() in functions with that from utils.misc

[hzovaro]

Closing for now.