TagPicker styleName attribute removes tag-picker styles

[Flaurite]

Description

Steps to reproduce

1. Configure TagPicker and add styleName in the XML:

   <tagPicker id="tagPicker"
          optionsContainer="orderLinesDc"
          stylename="medium"/>

2. Open screen and add some records to the field.

ER

AR

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QA

Additional to the case above:

1. Try to invoke getStyleName():

   notifications.create()
       .withCaption(tagPickerSimple.getStyleName())
       .show();

   The empty string or stylename (if it's defined) should be return.

[Flaurite]

Refactored get/set/remove style name methods to work the same as other components. QA description is updated.