contrib: push_locale.py: fix relative paths in messages_qml.pot

The Qt lupdate tool that extracts translatable strings from .qml files
writes paths relative to its output .ts file into the .ts file.
These paths are then retained as-is when converted to .pot format.

The last few commits moved around the working directory of the lupdate tool
(from electrum/locale to electrum/locale/build), which resulted in a change
of all relative paths in the final messages.pot we upload to crowdin.

E.g. from:
```
#: ../gui/qml/components/Addresses.qml:64
```
to:
```
#: ../../gui/qml/components/Addresses.qml:64
```

I think a change like this does not invalidate the translations. Still, it is annoying.

This commit adds an extra processing step to "fix" these strings to:
```
#: electrum/gui/qml/components/Addresses.qml:64
```

contrib/locale/push_locale.py

@@ -71,6 +71,7 @@ with open(f"{build_dir}/qml.lst", "wb") as f:
 
 print("Found {} QML files to translate".format(len(files.splitlines())))
 
+# note: lupdate writes relative paths into its output .ts file, relative to the .ts file itself :/
 cmd = [QT_LUPDATE, f"@{build_dir}/qml.lst","-ts", f"{build_dir}/qml.ts"]
 print('Collecting strings')
 subprocess.check_output(cmd)
@@ -79,6 +80,12 @@ cmd = [QT_LCONVERT, "-of", "po", "-o", f"{build_dir}/messages_qml.pot", f"{build
 print('Convert to gettext')
 subprocess.check_output(cmd)
 
+print("Fixing some paths in messages_qml.pot")
+#  sed from " ../../gui/qml/"
+#      to   " electrum/gui/qml/"
+cmd = ["sed", "-i", r"s/ ..\/..\/gui\/qml\// electrum\/gui\/qml\//g", f"{build_dir}/messages_qml.pot"]
+subprocess.check_output(cmd)
+
 cmd = ["msgcat", "-u", "-o", f"{build_dir}/messages.pot", f"{build_dir}/messages_gettext.pot", f"{build_dir}/messages_qml.pot"]
 print('Generate template')
 subprocess.check_output(cmd)