Modernized progress window GUI

Following the refactoring that has been initiated in pdfmasher's
"vala" branch, I pushed more progress window logic into the
core.

The UI code is now a bit dumber than it used to be, and the core
now directly decides when the progress window is shown and
hidden. The "job finished" notification is also directly sent by the
core. Job description update logic is handled by a core gui
textfield.

Job description contsants also moved to the core, triggering
a localisation migration from "ui" to "core".

locale/ui.pot

@@ -4,26 +4,6 @@ msgstr ""
 "Content-Type: text/plain; charset=utf-8\n"
 "Content-Transfer-Encoding: utf-8\n"
 
-#: cocoa/inter/app.py:15 qt/base/app.py:38
-msgid "Scanning for duplicates"
-msgstr ""
-
-#: cocoa/inter/app.py:16 qt/base/app.py:39
-msgid "Loading"
-msgstr ""
-
-#: cocoa/inter/app.py:17 qt/base/app.py:40
-msgid "Moving"
-msgstr ""
-
-#: cocoa/inter/app.py:18 qt/base/app.py:41
-msgid "Copying"
-msgstr ""
-
-#: cocoa/inter/app.py:19
-msgid "Sending to Trash"
-msgstr ""
-
 #: cocoa/inter/app_me.py:34
 msgid "Removing dead tracks from your iTunes Library"
 msgstr ""
@@ -75,10 +55,6 @@ msgstr ""
 msgid "The iPhoto application couldn't be found."
 msgstr ""
 
-#: qt/base/app.py:42
-msgid "Sending files to the recycle bin"
-msgstr ""
-
 #: qt/base/app.py:95
 msgid "Quit"
 msgstr ""
@@ -112,12 +88,6 @@ msgstr ""
 msgid "Open Debug Log"
 msgstr ""
 
-#: qt/base/app.py:217 cocoa/base/en.lproj/Localizable.strings:0
-msgid ""
-"A previous action is still hanging in there. You can't start a new one yet. "
-"Wait a few seconds, then try again."
-msgstr ""
-
 #: qt/base/app.py:257
 msgid "{} file (*.{})"
 msgstr ""