Add a protocol for making buffers

[kalekundert]

Buffers are similar to reactions, but there are a few noteworthy differences:

• I usually want to specify 1x concentrations (not volumes).
• I usually want to specify that the buffer should be concentrated, e.g. 2x, 10x, etc.
• I want the reaction table to show the 1x concentrations, but the 2x/10x/etc volumes (and maybe also the 2x/10x/etc concentrations). There are some examples of this style in ~dbp/protocols/recipes.
• Some extra steps, e.g. bring to certain pH before bringing to final volume.

This protocol should also integrate nicely with freezerbox. Right now I don't really use the buffers spreadsheet, but I think this is the missing piece.

I need to think about how to natually incorporate instructions regarding adjusting pH, volume.

[kalekundert]

It would also be nice to add to the config file a list of stock solutions. Freezerbox should be where all buffers are stored.

Each stock could also specify a one-letter abbreviation (e.g. 'T' for tris, 'S' for saline/NaCl, etc.) which could be used to construct short names (e.g. TGSV).