Fix user-facing misspellings

- Missing letter.

- Both '.json' and 'JSON' are used in other strings,
  but '.JSON' doesn't seem as clear.

- Fixed capitalization and added verb to ensure the sentence is readable.
  I don't think that reproducing the error message exactly
  helps making it more readable in this case, because it is unlikely
  that people reading it will recognize the capitals in the middle
  of the sentence as an exact quote of some program's output.

app/static/app/js/components/EditTaskPanel.jsx

@@ -53,7 +53,7 @@ class EditTaskPanel extends React.Component {
           this.setState({saving: false});
           this.props.onSave(json);
         }).fail(() => {
-          this.setState({saving: false, error: _("Could not update task information. Plese try again.")});
+          this.setState({saving: false, error: _("Could not update task information. Please try again.")});
         });     
     }
 

app/static/app/js/components/ProcessingNodeOption.jsx

@@ -159,7 +159,7 @@ class ProcessingNodeOption extends React.Component {
     let loadFileControl = "";
     if (this.supportsFileAPI() && this.props.domain === 'json'){
         loadFileControl = ([
-            <button key="btn" type="file" className="btn glyphicon glyphicon-import btn-primary" data-toggle="tooltip" data-placement="left" title={_("Click to import a .JSON file")} onClick={() => this.loadFile()}></button>,
+            <button key="btn" type="file" className="btn glyphicon glyphicon-import btn-primary" data-toggle="tooltip" data-placement="left" title={_("Click to import a JSON file")} onClick={() => this.loadFile()}></button>,
             <input key="file-ctrl" className="file-control" type="file" 
                 accept="text/plain,application/json,application/geo+json,.geojson"
                 onChange={this.handleFileSelect}

app/static/app/js/components/ProjectListItem.jsx

@@ -225,7 +225,7 @@ class ProjectListItem extends React.Component {
                             totalCount: this.state.upload.totalCount - 1,
                             totalBytes: this.state.upload.totalBytes - file.size
                         });
-                        throw new Error(interpolate(_('Cannot upload %(filename)s, File too Large! Default MaxFileSize is %(maxFileSize)s MB!'), { filename: file.name, maxFileSize: this.dz.options.maxFilesize }));
+                        throw new Error(interpolate(_('Cannot upload %(filename)s, file is too large! Default MaxFileSize is %(maxFileSize)s MB!'), { filename: file.name, maxFileSize: this.dz.options.maxFilesize }));
                     }
                     retry();
                 }else{