New:  common keywords used for all plugins that allow it

-- Rather than constantly having to repeat the keyword values on every
search you want to run, you can now just add a new
search_location_setting_set section in your INI file that defines all
the possible keyword values you want to search.  That set of values
will then be automatically applied to each job site you have listed to
search.  If the job site supports OR'ing terms, job_scooper will only
run one search with a multi-keyword string; otherwise it will run one
search per keyword in the set.

Example INI section:
[search_keyword_set]
keywords="director"
keywords="vice president"
keywords="product"
keywords="vp"
keywords="chief product officer"
keywords="Chief Technology Office"
keywords="CTO"
keywords="CPO"
keywords="senior manager"
keywords="general manager"

-- Note:  you can still specify a keywords="blah" value on a per search
basis.  Jobs_scooper will use that keyword value for that search
instead of using any keywords set.