libgui|RowAtlasAllocator: Improved row-based atlas allocator

This version is more intelligent in keeping track of empty space.
There is no longer a "rover", using which allocations are done in
sequence. Instead, all remaining empty space is partitioned (in rows)
to acquire a suitable block from the atlas.

Optimization is only done if there is a significant portion of
unused space.
liblegacy|Cleanup: Dumped the now unused v1 Kd Tree data structure
World|bsp::Partitioner: Cleanup
Renderer|Client: "Pixel Doubling" replaces the "Pixel Density" setting

Should be more intuitive this way. Also moved the setting under the
"Camera Lens" group (which could now use some subheadings/splitting,
perhaps).
Fixed|libgui|RowAtlasAllocator: Horizontal margin was ignored when allocating
libappfw|LogWidget: Removed the malfunctioning pausing mechanism

On second thought, this is not a good way to address the problem.
The widget should be skipping ahead instead of falling behind (cf.
dropping frames).
Cleanup
libappfw|LogWidget: Improved behavior during/after rewrapping

Fixes the issue where the scroll position would jump around
during/after resizing the log. However, now no attempt is made at
keeping the scroll position the same during rewrapping.
Fixed|Hexen|MP: Client crashes when a plane moves on client side

Some client mobjs don't have 'info' if they are only partially synced.

IssueID #1873
Fixed|World|Map: Missing return value in Map::forAllClusters()
World|Sector: Cleanup
Fixed|libappfw|HiDPI: Background blurring with high pixel densities

The blurring should account for the higher pixel density to achieve
a similar end result compared to regular density.
Cleanup: Removed obsolete "vid-*" cvars (resolution, fullscreen, bpp)

These are now configured via de::Config.
Fixed|World|bsp::Partitioner: Space partitioning results in superfluous line segments

An overly conservative epsilon used when searching for existing line
segments in the map would sometimes lead to the creation of additional
line segments unnecessarily.

IssueID #1591
World|bsp::Partitioner: Cleanup
Merge branch 'master' of github.com:skyjake/Doomsday-Engine
Fixed|All Games|SaveSlots: Resetting last-used and "quick" save slots on game change

When the game mode changes we should forget which save slots were
last-used/assigned-for-quick saving in process.
Tools|Amethyst: Updated for Qt 5
libcore|App: Accessing persistent data in read-only or mutable mode

Timestamps get updated automatically if the Archive is accessed in
mutable mode. Fixes a problem with Refuge (Config) where timestamps
were not being preserved even though no one had written to the archive.
libcore|Config: Check config script's package's timestamp

If the packages have been updated, read the config script just in
case. This makes things easier for developers when the scripts are
changed but the app version hasn't.

Added some utility methods to Package for finding the container
package of a file and checking its timestamp.