Fixes and improvements (#132)

- Fix glitch when turning on WiFi: It would temporarily show "No networks found" right before starting the first scan.
- Fix spinner to use Assets.h
- Replace statusbar battery icons 
- Better statusbar icon for when WiFi is on but not connected
- Replace statusbar WiFi icons and Wifi Manage RSSI/lock icons
- Fix for crash when timer is null in I2cScanner
- Deprecate Spacer
- Fixes for toolbar layout (simplified)
- Improved ImageViewer app: center image and add filename text on the bottom
- Add LV debug params to sdkconfig.developer
- Disabled LV spinner, msgbox and window widgets. These have equivalents in Tactility.

TactilityCore/Source/StringUtils.h

@@ -23,6 +23,12 @@ int findLastIndex(const char* text, size_t from_index, char find);
  */
 bool getPathParent(const char* path, char* output);
 
+/**
+ * Given a filesystem path as input, get the last segment of a path
+ * @param[in] path input path
+ */
+std::string getLastPathSegment(const std::string& path);
+
 /**
  * Splits the provided input into separate pieces with delimiter as separator text.
  * When the input string is empty, the output list will be empty too.