Use appropriate treeview row styling for Gtk+ version, fixes #4855

[samdroid-apps]

The older Gtk+ treeview css make the treeviews background single
colored on newer Gtk+. This patch discovers the Gtk+ version
through pkg-config as to introduce no new deps.

Ticket https://bugs.sugarlabs.org/ticket/4855

Replaces #74

[i5o]

Tested on sugar-build, broot mode.

[osbuild sugar-build]$ pkg-config --modversion gtk+-3.0
3.10.9
[osbuild sugar-build]$ lsb_release -a
LSB Version: :core-4.1-ia32:core-4.1-noarch
Distributor ID: Fedora
Description: Fedora release 20 (Heisenbug)
Release: 20
Codename: Heisenbug
[osbuild sugar-build]$

Doesn't broke the current model.
Will test ASAP on Fedora rawhide with mode_none

[i5o]

Tested on:

[ignacio@ignacio-pc ~] $ pkg-config --modversion gtk+-3.0
3.18.1
[ignacio@ignacio-pc ~] $ lsb_release -a
LSB Version:    :core-4.1-ia32:core-4.1-noarch:cxx-4.1-ia32:cxx-4.1-noarch:desktop-4.1-ia32:desktop-4.1-noarch:languages-4.1-ia32:languages-4.1-noarch:printing-4.1-ia32:printing-4.1-noarch
Distributor ID: Fedora
Description:    Fedora release 23 (Twenty Three)
Release:    23
Codename:   TwentyThree
[ignacio@ignacio-pc ~] $ 

Three test cases:
ListView, Treeview on Log activity, Journal activity.

patch not applied:

Patch applied: