add php-intl check (#95)

[fritzmg]

This adds an additional check for the PHP Intl Extension (see #95). Again, this PR comes without any translations.

[leofeyer]

I cannot merge the PR like this.

On the start page of the check, only the PHP versions are checked. If you want to check for PHP extensions, you would have to add a details page (as for the file permissions, the repository etc.).

[fritzmg]

Yes, but currently, none of the compatibility checks for Contao have something like that. Should it only be added for Contao 4?

[leofeyer]

It does not have to be added at all IMO. But if you still want to, you would ideally do it for all Contao versions; whereby we can remove the Contao 2 check I guess.

[fritzmg]

It does not have to be added at all IMO.

Well it would be helpful. The following procedure is described quite frequently on the community forum:

1. Users upload the Contao Check to their webspace, where they are told that they can install Contao 4.
2. They download Contao 4 from contao.org and put it on their webspace.
3. They open /install.php, enter the Install Tool password and after that are presented with a blank page.
4. Since there is no visible error message, nor will there be an entry in /app/logs, they wonder why it's not working.

In most cases it's the missing PHP Intl extension.

[fritzmg]

I have created a more detailed PR: #108

[leofeyer]

So can this one be closed?

[fritzmg]

Yes