Update figures 1, 2, and 3 for SDx 2019.1 (#471)

* Update gui_fig_2.png and gui_fig_3.png to SDx 2019.1
SDx's welcome screen has stratified the option (read: clickable button)
to `Create SDx Project` into two new ones: `Create Platform Project`
and `Create Library Project`.  These changes are rendered in Figure 2,
while Figure 3 captures cosmetic differences to the user interface.

* Add Figure 2

* Add Figure 3

Author: Kenso Trabing

SDAccel/docs/README_GUI.md

@@ -62,7 +62,7 @@ We will now cover the following steps:
 Add workspace inside the current directory named "GUI_test" as shown below. A new directory **GUI_test** will be created and used to store all logfiles of our runs.  
 
 
-![](./figure/gui_fig_1.JPG)  
+![](./figure/gui_fig_1.png)  
 
 <br>
 
@@ -71,15 +71,15 @@ You will get a Welcome screen. You need to set Platform path by selecting **Add
 
 <br> 
 
-![](./figure/gui_fig_2.JPG)  
+![](./figure/gui_fig_2.png)  
 
 
 
 Click on the **plus** sign as shown below.   
 
 
 
-![](./figure/gui_fig_3.JPG)  
+![](./figure/gui_fig_3.png)