Change capability for EDD Add Ons and System Info sub menus

The "install_plugins" capability gives only WP super admins on WP multisite installs access to Add Ons, System Info Upgrade screen.
This is how it should be.
On single WP installs the Admin still can access these sub menus.
see
http://codex.wordpress.org/Roles_and_Capabilities
Whitespace
Ensure htaccess rules are flushed on settings save. #1270
Update version numbers and changelog for v1.6.4
Fix for #1309
Merge pull request #1313 from ghost1227/master

Fix for #1309
Merge pull request #1291 from robaggior/patch-2

Change capability for EDD Add Ons and System Info sub menus
Undeprecate edd_count_payments and refactor to allow it to count payments based on user. #1310
UPdated phpdoc and removed test print. #1310
Correct counts when searching. #1310
Tweak non-email and non-purchase key search. #1310
Add comments. #1310
Merge pull request #1316 from easydigitaldownloads/bug/payment-counts

Bug/payment counts