Skip network installation on large networks

When network activating on large networks, we don’t attempt to do the
per-site installation. We also show the user a notice, telling them of
this.

See #68
Skip per-site uninstall on large networks

See #68
Skip points component uninstall on large networks

We skip the per-site uninstallation of the points component when
uninstalling on a large network.

See #68
s/install/uninstall/

See #68
Skip updates on large networks

And show the user a message when we do.

See #68
Skip points component updates on large networks

Don’t attempt to update the points component per-site on large networks
when the plugin is network-active.

See #68
Use *_metadata() function in the log meta funcs

Fixes #109
Merge branch 'issue-109'
Update uninstall plugin tester

So we can use the no site options assertion.

See #68
Introduce new un/installer class

And update the unit tests.

This implements code which keeps track of which sites the plugin is
installed on on multisite, and only attempts to uninstall from those
(unless it has been network-activated).

See #68
Include un/install class for modules & components

See #68
Don't try to skip uninstalling points component

We were previously attempting to detect if it was installed, and only
run the uninstaller if so. That’s not reliable, because of the use of
WordPoints “network” option feature. This selects a regular or site
option based on how WordPoints is activated, but it isn’t possible to
determine that on uninstall, since the plugin isn’t active at all.

See #68
Add install_*() as abstract on base un/installer

See #68
Document the $capabilities property

See #68
Still use $network_active in install file

It is a required argument of `wordpoints_activate()`.

See #68
Use the correct l10n function

See #68
Update the l10n validator config

See #68
Un/installer: add option_prefix property

In favor of several option properties.

See #68
Include WP's upgrade script during install

Makes `dbDeleta()` available for creating databases.

See #68
Un/installer: add a before_install() method

See #68