GRAN packages that depend on other GRAN packages

[ldecicco-USGS]

The order of the package installation is alphabetical. If a package (DVstats for example) requires a package (smwrStats)....we need to install smwrStats first.

Ideally, no packages should have circular dependencies.....I'd almost not bother trying to bombproof this system to handle that.

But...there are plenty of packages in GRAN that depend on each other. We need to either have a way to specify order, or do the order in the same way as the gran_source_list.tsv.

One thing that can help in the meantime is to do the gran build for each pull request (at least via Jenkins), rather than merging all the PR's for 1 week, and doing it once. Then, if there are new packages...we can monitor (more) easily if they depend on each other.

[ldecicco-USGS]

Oops, same as #19

[ldecicco-USGS]

Build the dependency tree and flatten to the right order.

[jiwalker-usgs]

Just a couple notes in looking at this. We should be able to build the dependency graph using miniCRAN, and then peel off the dependencies (may need to deal with cycles yet) using igraph functions. I'd like to be able to sneak non-published packages into this by reading the DESCRIPTION file directly. One thing I found that can help with that is the read.dcf function which is used under the hood of pkgDepends used by miniCRAN.

[ldecicco-USGS]

Need to flag error, and deal with cyclic dependencies