Implemented several changes to close issues regarding enhancements

1. Renamed variables in dose files as re-factoring to avoid confusion (See commit: ee8b125963165ae7722f5912659a2c4cc744651e, 1bc748f4f3a91f53067f1858252bb3ad47801027, ba92e3ef05158d8f5716d869aedde2815c6fcab7 and 459e36a28dcf48645dfc61b6ffe77435fc2bc150)

2. Hid dose_world initialization inside dose.py's dose_functions (See commit: 956f479bfd781f6448e8443ac570edf9b9c14e0a)

3. Merged eco_cell_locator and eco_cell_executor due to redundancy (See commit: c8d9e9d46e7c2b183cd4b98060de07cf808829be)

4. Implemented helper functions that filter the population based on a specific status dictionary key (See commit: 3644dee08ae93812ecd7828dd99a4616741685e6)

5. Added method to enable user to define custom-deployment schemes (See commit: 3ec4e98fe61f3d6be4bfbb01953f21e3f6fd23ef)