Timber: Provide proper upgrade guidance in admin depending on installation method

[jarednova]

This is a todo based on @gsalkin's comments in #1673 — basically we should properly message upgrade procedure in WP Admin based on how Timber was installed (Composer vs. WP.org)

[gsalkin]

I would modify requirements for timber-library 2.0 to also require Twig 2.x. Currently timber-library still calls for the deprecated version of Twig. Now that most installations support PHP 7.x, I would move users to have that installed.

Creates better parity between the Github version and WordPress plugin.

[gchtr]

A quick note: Bumping the minimum Twig version to 2.x would probably break compatibility with WPML. WPML still uses Twig 1.32.0 (for compatibility with PHP5) and also loads Twig through Composer. Currently, the only solution I found to make WPML work with Timber is to install Timber as a plugin (related: #1064). But then, WPML’s Twig version will be used instead of Timber’s, which is not future-proof either.

I’m all for parity. I’m not saying we shouldn’t upgrade the minimum requirements (I’m not a big fan of WPML myself 🙊), but if we do it, we probably need to mark Timber as incompatible with WPML.

[jarednova]

Gahhhhhh!!!!!! Twig!!!!!

[gchtr]

I guess this can be closed. We won’t release 2.x as a plugin, but only as a Composer package. See #2005.