Add QR code generator for TOTP export (#1167)

* Resolves #764
* Add libqrencode and qtsvg dependencies 
* Ensure QR code remains square
* Auto-close QR code dialog when database is locked
* Add databaseLocked() Signal to databaseWidget
* Correct otpauth URI output in Totp::writeSettings(...)

ci/trusty/Dockerfile

@@ -18,7 +18,7 @@
 
 FROM ubuntu:14.04
 
-ENV REBUILD_COUNTER=4
+ENV REBUILD_COUNTER=5
 
 ENV QT5_VERSION=qt53
 ENV QT5_PPA_VERSION=${QT5_VERSION}2
@@ -49,11 +49,13 @@ RUN set -x \
         ${QT5_VERSION}tools \
         ${QT5_VERSION}x11extras \
         ${QT5_VERSION}translations \
+        ${QT5_VERSION}svg \
         zlib1g-dev \
         libyubikey-dev \
         libykpers-1-dev \
         libxi-dev \
         libxtst-dev \
+        libqrencode-dev \
         xvfb
 
 ENV PATH="/opt/${QT5_VERSION}/bin:${PATH}"