display server selection in list or selectbox form, or option tags only

• uses: implode()
• uses: PMA_generate_common_hidden_inputs()
• uses: PMA_generate_common_url()
• uses: htmlspecialchars()
• uses: $GLOBALS['strServer']
• uses: $GLOBALS['cfg']['Servers']
• uses: $GLOBALS['strGo']
• uses: $GLOBALS['cfg']['DisplayServersList']

• boolean $not_only_options: whether to include form tags or not
• boolean $ommit_fieldset: whether to ommit fieldset tag or not