Clean and integrate Doubling time code and outputs

[MGMD-96]

v1: Doubling time code (dev by @TechnoSAP) and output (dbt.json) added to reproduction-number-rt folder in repo.

For doubling time script

• Change source API to the new one (data-all.json). This script uses cumulative confirmed cases timeseries. Input cumulative confirmed cases data from new source API in cumul_cases = in both India and States script inside doublingtime.ipynb
  (shift to new API necessary so that same code can also run on districts)
• Implement global dictionary for dates
• In the output json (dbt.json), some values of doubling time are Infinity or Nan. These output values to be replaced by empty value "" otherwise will interrupt plotting later.
• Integrate this script into an existing script. (posrate) (@siddharthjain1611 will decide). Also output into existing json (posrate).
• Add code to output dbt into csv as well (posrate csv).

For Rt script

• Change source API to the new one (data-all.json). This script uses daily confirmed cases timeseries. (shift to new API necessary so that same code can also run on districts)