added comments and changed export filenames

minor aesthetic changes
1st commit: proxy vax eff w/ susceptibility

added new percolation function to percolations.py with:
- 2 vax coverage scenarios (0.245 and 0.455)
- susceptibility multiplied by T for vax individuals

age_perc_vaxeff.py script:
- plots OR vs. vax efficacy where vax efficacy is
defined as 1 - susceptibility
- exports simulation data into 4 separate files
- plots diagnostics of episize vs. vax efficacy
and number of epidemics vs. vax efficacy
added comments, changed export filename
added plt.close() line so plots print correctly
add code for diagnostic plots

diagnostic plots include:
episize with error bars by vax coverage
number of epidemics by vax coverage
changed export file name error

error was found in figname for epidemic size
diagnostic plot