Calendar: Show multi-day event continuation

Currently, multi-day events are shown as individual appointments on each
day.  This patch ellipsizes multi-day events to indicate continuation on
the prior or following day (or other time-period.)

The time label spot is now replaced by a box layout that contains the
prefix ellipsis label, the time label and the postfix ellipsis label.
In order to keep the alignment, ellipses are merely invisible (zero
opacity) when hidden.

The ellipses are styled using the events-day-time-ellipses class which,
by default, take the color of the event text.

When RTL is used, the box contents are adjusted accordingly (clutter
does that for us).

An event spanning three days now displays "...All Day..." in the
calendar on the second day.

https://bugzilla.gnome.org/show_bug.cgi?id=727302
Calendar: sort multi-day events by ending day/time

With commit dc6a60dde, the calendar displays the ending day and time of
a continuing multi-day event on its ending day. This results in the list
not appearing to be sorted. This patch sorts the list according to the
displayed day/time.

With the two appointments
Thursday 0800-1000 Foo, and Wednesday 0900-Friday 1200 Bar and today
being Monday, the rest of the week list currently displays:
F ...1200 Bar
T    0800 Foo
With this patch, the displaying order is switched because Friday comes
after Thursday.

https://bugzilla.gnome.org/show_bug.cgi?id=727302
Calendar: Inline _ellipsizeEventTime into caller

This patch inlines the function _ellipsizeEventTime into its only caller
_addEvent. This also removes the need for the global const
EventEllipses and is thus removed by this commit as well.

https://bugzilla.gnome.org/show_bug.cgi?id=727302
scroll-view: Support GTK_POLICY_EXTERNAL

GTK+ added a new PolicyType which currently triggers compiler warnings
about unhandled values in switch statements. We also have a use case for
it already, so add support for the new policy type.

https://bugzilla.gnome.org/show_bug.cgi?id=739379
appDisplay: Use EXTERNAL scroll policy

Now that we support the new policy type, we can just use it instead
of hiding the scrollbar.

https://bugzilla.gnome.org/show_bug.cgi?id=739379
Bump version to 3.15.1

Update NEWS.
build: Bump GTK+ requirement

GTK_POLICY_EXTERNAL requires at least 3.15.0
dateMenu: Fix typo in _isToday()

getDay() is the day of week, what we want there is getDate().

https://bugzilla.gnome.org/show_bug.cgi?id=738725
Update Aragonese translation
Move style updates in AppIcon._onStateChanged out

There is currently no simple way to inject into AppIcon's state change,
so an extension that wants to do this has to destroy/remove/update all
icons in the Shell (i.e. in the Dash, AllView, FrequentView) on enable()
and disable() after updating AppIcon.prototype._onStateChange, or the
extension must require a restart of the Shell.

To solve this issue, we rename _onStateChanged to _updateRunningStyle,
and connect the notify::state signal with an anonymous function that
calls _updateRunningStyle.
This extra function call should allow extensions to just extend the
updateRunningStyle function in the prototype.

https://bugzilla.gnome.org/show_bug.cgi?id=739497
css: Add an inset shadow to overview windows

A small dark gap was caused by the rounded window edges not meeting the
sharp corner of the CSS border on hover. By adding a small inset
box-shadow, this gap is filled in.

https://bugzilla.gnome.org/show_bug.cgi?id=699044
portalHelper: Change user facing name to "Network Login"

"Captive Portal" is a bit confusing for people who are not familiar
with the technical term.

https://bugzilla.gnome.org/show_bug.cgi?id=737198
build: Workaround quoting issues in configure script

Default value of BROWSER_PLUGIN_DIR variable contains special symbols.
Thus quoting and inlining it in parameter expansion is not portable.
In particular it does not work in dash. Replace ${a:-b} parameter
expansion with conditional statement.

https://bugzilla.gnome.org/show_bug.cgi?id=739241
st-button: Recognise all Enter keys as Return

Bug #704339.
screenShield: Recognise all Enter keys as Return

Bug #704339.
Port gnome-shell to Python 3

https://bugzilla.gnome.org/show_bug.cgi?id=732478
rfkill: remove unused code

https://bugzilla.gnome.org/show_bug.cgi?id=736292
rfkill: hide Airplane Mode indicator when g-s-d says so

https://bugzilla.gnome.org/show_bug.cgi?id=736292
dateMenu: Allow extensions to add custom calendar sources

Splits instantiation of the event source into a separate method,
allowing extensions to subclass the DateMenuButton and provide its
own calendar source.

https://bugzilla.gnome.org/show_bug.cgi?id=672500
Calendar: Remove leading zeros for 24h time format

https://bugzilla.gnome.org/show_bug.cgi?id=658675