core: introduce g_paste_item_get_real_value

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
core: use get_real_value where appropriate

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
core: ignore password items for growing lines

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
core: override get_value in password item

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>