Add always_wrap_multiple_from setting.

[carljm]

At Instagram we would like to switch to isort to enforce our imports coding style, but our style requires use of the "vertical - hanging indent" style for all import from statements with multiple names imported. It doesn't matter how long they would be on a single line, they should always be wrapped with each imported name on its own line. E.g. even if from foo import bar, baz easily fits within 80 characters, we always write it as:

from foo import (
    bar,
    baz,
)

The reason for this is that it minimizes pollution of git annotate and makes it easier to track down who added/removed a single import, and when.

This pull request adds an always_wrap_multiple_from boolean setting which implements this.

[ryabtsev]

A similar setting is already there: "force_grid_wrap" (force from imports to be grid wrapped regardless of line length)

[carljm]

@ryabtsev Thanks! Looks like force_grid_wrap=true along with multi_line_output=3 does exactly what I want; just mis-led by "grid" in the setting name.