Add HtmlFormBuilder

Relates to #537 

`HtmlFormBuilder` to easily create a form using a fluid interface and avoid
things like `'<form name="searchbyproperty" action="' . '" method="get">' . "\n" . ...` within a script to avoid manual templates.

```php
$html = $htmlFormBuilder
	->setName( 'searchbyproperty' )
	->withFieldset()
	->setParagraph( $resultMessage )
	->setPaging(
		$this->queryOptions->limit,
		$this->queryOptions->offset,
		$resultCount )
	->setHorizontalRule()
	->setInputField(
		$this->messageBuilder->getMessage( 'smw_sbv_property' )->text(),
		'property',
		$this->queryOptions->propertyString,
		'smw-property-input' )
	->setNonBreakingSpace()
	->setInputField(
		$this->messageBuilder->getMessage( 'smw_sbv_value' )->text(),
		'value',
		$this->queryOptions->valueString,
		'smw-value-input' )
	->setNonBreakingSpace()
	->setSubmitButton( $this->messageBuilder->getMessage( 'smw_sbv_submit' )->text() )
	->getForm();
```
```php
$html = $this->htmlFormBuilder
	->setName( 'buildtables' )
	->setMethod( 'post' )
	->setParagraph( $this->messageBuilder->getMessage( 'smw_smwadmin_docu' )->text() )
	->setHiddenField( 'action', 'updatetables' )
	->setHeader( 'h2', $this->messageBuilder->getMessage( 'smw_smwadmin_db' )->text() )
	->setParagraph( $this->messageBuilder->getMessage( 'smw_smwadmin_dbdocu' )->text() )
	->setParagraph( $this->messageBuilder->getMessage( 'smw_smwadmin_permissionswarn' )->text() )
	->setHiddenField( 'udsure', 'yes' )
	->setSubmitButton( $this->messageBuilder->getMessage( 'smw_smwadmin_dbbutton' )->text() )
	->getForm();
```

The final form (as `string` representation) is generated when `getForm` is called and by doing so all existing parameters and variables are reset to a default value.
Since this thing is fully disjoint from the application domain of SMW, have you considered putting this into its own library? Just this alone might not be worth the effort, though I suspect there are other candidate classes as well that would form a cohesive package.