Use the correct variable, instead of the entire QStringList, to fill in

lineedit's text in autoDetectSystemProxy().
When saving for "System Proxy" configuration be sure to write the name
of environment variables and not their values in the configuration file.
Added missing signal connection for mUi.systemProxyRadioButton.
Connect slotChanged() to textEdited() signal, instead of textChanged(),
for systemProxy's lineedits: this avoid to emit changed() when
"Show the value of the envirnment variables" checkbox is clicked.

BUG: 304707
FIXED-IN: 4.11.3
REVIEW: 113129