DolphinQt: About dialog fixes, SystemInfo dialog

Example output:
```
System
===========================
OS: Windows 7
CPU: AMD Phenom(tm) II X4 925 Processor (AuthenticAMD), SSE, SSE2, SSE3, 64-bit support, 4 cores

Dolphin
===========================
SCM: branch dolphin-qt, rev 51700a2b6873b698e7d446c73a519bf5e9e863ee
Compiled: Oct 24 2014, 16:11:36

GUI
===========================
Compiled for Qt: 5.3.1
Running on Qt: 5.3.1
```

Note I had to fix the CPU brand/cpuid reversal in 51700a2b6873b698e7d446c73a519bf5e9e863ee in order for this to work. Also, the core count is determined using `QThread::idealThreadCount()`.

Review? @lioncash @comex @shuffle2 
As previously discussed, I'm using `parent_widget` as `parent` shadows a member of the `QObject` class which spams warnings. `MainWindow` already does the same.