Update index.php

[Assimilationstheorie]

Remove Short-Opentags, because the option "--enable-short-tags" in php.ini are not unique configured...
Add simple HTML-Validation with "required"
Submit Button without value-att. are not cool!

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[Assimilationstheorie]

I signed it!

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CLAs look good, thanks!

[bshaffer]

As mentioned in this comment, <?= is ok and we are keeping them.

I have never heard that a submit button without the value attribute is bad practice. Can you please point me to some resources saying so?

Adding the required tag is okay, but these samples are meant to be kept as simple as possible, so I am not really a fan. However, if you remove all the other stuff we can merge that.

[bshaffer]

Closing so that we can roll these changes into #1456