Original PR description

### Issue

	- Install Website Live Chat
	- Go on your website
	- Open livechat

	The composer is a simple textarea without any style.

### Cause

	According to the code, the initial idea was to re-use
	the already existing CSS code for the chatter composer.

	But it is not the case, because there are missing css
	files and the structure is incorrect.

### Solution

	Import the CSS files, fix the structure and add a new
	class "o_customer_composer" to add styles only to this
	composer. (e.g. the height, because in the chatter
	composer, it's computed by the JS)

**OPW-2179519**

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