setStyleSheet was overriding default tooltip theme from the system,
causing themes like Breeze to render white text on a grey bg for
tooltips. Tooltips now render default for the system theme everywhere.

set a theme matching color on the dark theme comboboxes.

fixes #118

Replace QHBoxLayout with QFormLayout in UserSettings

Use Nico's suggestion to just leverage the width of the field, and leave
a comment.

don't use members format camelCaseTail_

to save on recalculation of the size and having to subtract the margins
to do the tally, then re-apply.

Removed empty labels in favour of a fixed height and bottom alignment.

use QString instead of std::string (QStringLiteral doesn't have a
constructor with int, str.)

remove temp variable, and just deal with it inline.

Add Ubuntu 19.10 build requirements to README

 - Switch to {} widget initialization
 - set fixed size on the Toggles so they don't scale down vertically
 - add another setting section for INTERFACE
 - add a placeholder value for deviceFingerprintValue_ so it can calculate the right size.
 - fix warnings about `QLayout: Attempting to add QLayout "" to UserSettingsPage "",` in boxWrap
 - hide widgets properly in Q_OS_MAC
 - remove mainLayout_ completely
 - clean up resizeEvent

This allows form fields to wrap dynamically when they are too long for
the view. This should help mobile and small screen users to configure
the app without having to force it into portrait mode, or not be able to
reach the settings fields at all.

use the standard system download path for file downloads

QFileDialog's dir arg (which was set to the incoming file name from the
Matrix download) can take a full path to suggest. By prepending
QStandardPaths::DownloadLocation, it opens to the system's download
folder and proposes the filename as the download name.

Using QStandardPaths should make this work on other platforms, and from
what I read, its possible for this to return an empty string on
platforms where it doesn't support it, so this should essentially
revert to the previous functionality if Qt can't determine the system's
download location.

Add Japanese translation

markdown -> Markdown

Fix image overlay appearing on the wrong screen.

thanks adasauce!

it was causing the full screen image overlay to appear on the "primary
display" vs. the actual display nheko is running on.

removing the move() call makes the overlay follow the window.

The ISO 639-1 code of Japanese is not "jp" but "ja".