[s]: display exception raised when loading theme

[cbenz]

Found that while working on a theme: error stack trace was not displayed.

I reproduced the way plugin errors are displayed

frontend-v2/utils/index.js

Line 274 in dcbafc5

console.warn('WARNING: Failed to load configured plugins', plugins, e)

Before:

Loading configured theme...                                                                                                                   
ckan-ng-theme-xxx                                                                                                                           
WARNING: Failed to load theme -- ckan-ng-theme-xxx                                                                                          
Loading configured plugins...                                                                                                                 
Listening on :4000                                                                                                                            

After:

Loading configured theme...                                                                                                                   
ckan-ng-theme-xxx                                                                                                                          
Loading configured plugins...                                                                                                                 
Listening on :4000                                                                                                                            
(node:8540) UnhandledPromiseRejectionWarning: ReferenceError: utils is not defined                                                            
    at app.get (/home/cbenz/Dev/datopian/frontend-v2/themes/ckan-ng-theme-xxx/index.js:54:22)                                               
    at process._tickCallback (internal/process/next_tick.js:68:7)                                                                             
(node:8540) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async functio
n without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)                                     
(node:8540) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled 
will terminate the Node.js process with a non-zero exit code.                                                                                 

[anuveyatsu]

Cool 👍 thanks!