add constants to drake

[russellhz]

add constants to drake to ensure that any changes to constants.R will be captured.

This works by cleaning the entire cache if constants has been changed (and it is not the first time drake is being used). A message is written out to inform the users

[codecov[bot]]

Codecov Report

Merging #1195 (9cb0eb7) into develop (5483d25) will increase coverage by 0.00%. The diff coverage is 100.00%.

:exclamation: Current head 9cb0eb7 differs from pull request most recent head aa135e5. Consider uploading reports for the commit aa135e5 to get more accurate results

@@           Coverage Diff            @@
##           develop    #1195   +/-   ##
========================================
  Coverage    95.49%   95.49%           
========================================
  Files          362      362           
  Lines        55142    55137    -5     
========================================
- Hits         52656    52652    -4     
+ Misses        2486     2485    -1     

Impacted Files	Coverage Δ
R/driver.R	85.19% <100.00%> (+0.29%)	:arrow_up:
R/zchunk_L231.proc_sector.R	91.92% <0.00%> (-0.18%)	:arrow_down:
R/zchunk_L241.fgas.R	100.00% <0.00%> (+0.64%)	:arrow_up:

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[russellhz]

note that failures are just due to failing old-new, which is from previous PRs