Multisite setup improvements

[danepowell]

Just capturing some of the friction points I encountered while setting up multisite.

1. I've documented the basic setup process in Document multisite setup process #1027, but I think a lot of these steps could be automated with a simple multisite setup command. This could copy directories and settings files, create aliases, and set $site_dir to start with (see next).
2. Right now $site_dir needs to be manually set and is used to set a bunch of other configs (such as public files path). It seems like it would be pretty easy to set this automatically. Connects to #1028: Auto-discovery of $site_dir #1086
3. Right now all settings files are duplicated between every site in the codebase. This makes updating these files non trivial and very error prone. It would be better if generic settings could go into sites/all or get symlinked to a master copy in sites/default or something along those lines. EDIT: actually the BLT settings.php includes are hardcoded to pull from sites/default/settings/*. Which I guess sort of solves this problem, it just wasn't what I was expecting.

[grasmash]

@danepowell Can you point me to the code that you're referencing here?

Actually the BLT settings.php includes are hardcoded to pull from sites/default/settings/*. Which I guess sort of solves this problem, it just wasn't what I was expecting.

Can we consider the third point complete?

[danepowell]

Yeah, I wasn't even really referring to BLT... each project can decide how they want to pull in any other settings files. I don't think BLT needs to worry about it.

[grasmash]

Cool. Other issues addressed!