bitbake: hob: create save image dialog used to save a template

Implemented a new dialog used by Hob. This dialog was desinged
in order to permit to save only in a particular directory.
Also, it has a field where the user can type a description
for the image.
Implemented in the handler a method to retrieve the topdir variable,
because the changes will be saved in {topdir}/recipes/images directory.

[YOCTO #4193]
(Bitbake rev: 117d4809a62e28ffe7e9dcda5433993d76f7d934)

Signed-off-by: Cristiana Voicu <cristiana.voicu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/ui/crumbs/hobeventhandler.py

@@ -452,6 +452,9 @@ class HobHandler(gobject.GObject):
     def get_logfile(self):
         return self.server.runCommand(["getVariable", "BB_CONSOLELOG"])[0]
 
+    def get_topdir(self):
+        return self.runCommand(["getVariable", "TOPDIR"]) or ""
+
     def _remove_redundant(self, string):
         ret = []
         for i in string.split():