saving indicator

[kfarr]

After pressing "Save" or "Save as..." to save to cloud, indicate to the user that saving is in progress and do not allow user to press save or save as buttons again until done.

v1 - use saving loader we created long ago
v2 (later ticket) instead only show loader / deactivate save button while keeping rest of the editor active

for v1 use existing saving modal

• https://github.com/3DStreet/3dstreet-editor/tree/master/src/components/modals/SavingModal
• used once for save indicator while capturing scene until we fixed the delay, can take over that state isCapturingScreen to rename as isSavingScene if we want to use that toolbar state
• Example of previous usage: fa8c197

[kfarr]

#298