Introduce get_rewrite_regex() method
Remove our rewrite rule before flushing upon plugin deactivation
Require network-activation of Proper Network Activation plugin before
network-activating Dependency Minification
Revert "Require network-activation of Proper Network Activation plugin before"

This reverts commit 5fc61bc9748dd79f722bc97bb2e610ab85e84c63.
Add info about network activation in plugin description
Make PNA links open in a new window
Merge pull request #37 from x-team/issue-37

Improve network activation and deactivation

* Flush rewrite rules network-wide when network-activated
* Prompt for installing @scribu's Proper Network Activation plugin