Refactor/data processing empowerment

[pausz]

Brief description

Splits large R script into three independent scripts that preprocess data for:

• age at first partnership/cohabitation
• empowerment
• education
  • updates kenya/data/edu_stop.csv because the refactored R script fills out the 'percent' column with zeroes for some ages that were note represented in pma dta files.

Type(s) of change

• Bugfix
• Refactor
• New feature
• Other

Checklist

• My code follows the style guide
  • Yes
  • N/A
• I've commented my code
  • Yes
  • N/A
• I've incremented the version number
  • Yes
  • N/A
• I've updated the changelog
  • Yes
  • N/A
• I've added tests and checked code coverage
  • Yes
  • N/A