[Develop] Turn parent menu slug into a config variable

[jrfnl]

Allows for setting of the parent menu item from the $config array

[jrfnl]

@thomasgriffin Any feedback on this ?

[senlin]

This looks great, would be awesome if it can be integrated. Thanks!

[jrfnl]

@senlin Glad you like it ;-)

@thomasgriffin I kind of have the feeling that you may be hesitant about this PR because it builds on the changes from @zackkatz's PR #188 which were merged in develop, but not in master because of the theme check disallowing the use of add_submenu_page().

I think I can provide a solution.

A while ago, I send in PR #219 with some changes to allow for overloading of the class. If that PR would be merged, we can then leave the 'old' method in the base class which would be used by themes.
For plugins which may want to change where the menu is added, an overloaded class can be added which adjusts the admin_menu() method to use add_submenu_page() instead.

I might need to still make some small changes to the code in #219 to make this more intuitive for less experienced programmers, but would like your opinion before I spend a lot (more) time on something which may never get accepted.

So what do you think ?

[jrfnl]

Also: the current getting of the admin page with the code in the develop branch what with the hard-coded themes.php, only works because of a recognized bug in WP. We can't count on the bug staying in.
Ref: https://core.trac.wordpress.org/ticket/28821

[GaryJones]

+1 for abstracting 'themes.php'.

0 (but willing to be swayed) for making them properties as well. What's the reasoning there? To be able to subclass? (If so, how does that handle with the main class being a singleton?)

[jrfnl]

0 (but willing to be swayed) for making them properties as well. What's the reasoning there? To be able to subclass? (If so, how does that handle with the main class being a singleton?)

@GaryJones I followed the logic which was already in place - the TGM_Plugin_Activation::config() method currently sets all config variables passed as properties, i.e. the properties have to be there.

[GaryJones]

+1 for being consistent then :-)

[jrfnl]

Related #65

[jrfnl]

Related 44228af and 5c76406 which seem to be reversed/taken out by c44d6aa