Expand check_tcpl_db_schema() for more kinds of backwards compatibility related checks

[cthunes]

Some ideas for how we could use check_tcpl_db_schema(), returns are when using current (unreleased 4.2) invitrodb schema.

check_tcpl_db_schema()
# TRUE

# returns list of available fields in mc4 in current db version
check_tcpl_db_schema(tbl = "mc4")
# c("m4id", "aeid", "spid", "bmad", "resp_max", ...etc)

# checks whether the given field is available in the current db schema, looks within a kind of dictionary or map for what the field name is in the given schema
check_tcpl_db_schema(fld = "logc")
# "conc"
check_tcpl_db_schema(fld = "conc")
# "conc"
check_tcpl_db_schema(fld = "modl_ga")
# "ac50"
check_tcpl_db_schema(fld = "ac50")
# "ac50"

Future tickets could look into updating functions to use these new enhancements.