Correctly expand list of nearby people to the entire height of the screen.

NOTE: To be cherry-picked into stable-v0.100

If the device is small, then the "Conenct and trade apps with people near you" header takes up too much space and we end up not being able to see any nearby people at all, even if they are in the list. As such, this also removes that header for "small" and "ldpi" devices. During testing I found that "small" was not enough, because a 240x400 screen is considered "medium" and there is not enough space. ldpi seems to be a reasonable metric for "that header is going to be taking valuable space and should not be shown then".

All larger devices retain the header and seem to look nice.

This also pushes the "Can't find what you're looking for?" message and associated buttons right to the bottom of the screen. This is more in line with the original design.

Fixes #604 (closed).

Screenshots

No good

The image below shows a 240x400 device. This falls into the "medium" screen size, and so would include the header if I only used "layout-small". As such, I also removed the header for "layout-ldpi". It doesn't look absolutely terrible, but remember that this is an emulator without Bluetooth, and as such it is missing a UI element for enablign Bluetooth which would take up the remaining real estate:

emu-240x400

Good

Large devices work well now, with all of the empty space below available for the "Nearby Devices":

large_device

Also, small devices should exclude the header and provide just enough space for the list of pears (as shon by this 240x320 device):

emu-240x320dp

Here is a more normal sized phone (my Moto X 2nd gen with normal DPI settings):

moto_x_2nd_gen__largish_