hob: Buttons width and height are taken for host

hob: Buttons width and height are taken for host

- removed all set_size_request calls for buttons in order to:
	- force autosizing of buttons with regard to the text length
	- use host theme default height for buttons
- modified buttons on image details page to have the same height (default host one) and the width of the button with the largest text
- modified Stop button on build details page to have the default height by directly attaching it to the containing table instead of hbox

Signed-off-by: Ioana Grigoropol <ioanax.grigoropol@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>