New gadget button "Locked"

[Ranran(retired)]

Pull request #397:
This is the extended version of the features posted here.

The patch contains an updated New standard theme for testing new gadget icons.
If the theme does not have a lock icon, the letters "L" and "l" will be displayed instead.
This behavior is the same as if the existing gadget does not have its icon.

[Ranran(retired)]

This thread is located in Incorporated patches/merged pull requests board, but it was actually lost during the mass merge turmoil and has not yet been merged.
So I threw a pull request again. Please check #417.

[jamespetts]

Thank you - now incorporated.

[Ranran(retired)]

The gadget symbol is so small that it's hard to tell if it's locked.
The pull request #427, unearthed on Friday the 13th, improves the visibility and security.

[jamespetts]

The gadget symbol is so small that it's hard to tell if it's locked.
The pull request #427, unearthed on Friday the 13th, improves the visibility and security.

Thank you - now incorporated.

[Ranran(retired)]

I found a bug. (´・ω・｀)
Locked dialogs could remain beyond the save and cause it to crash. So when open a banner or save/load dialog, simutrans have to kill all dialogs, even if it's locked.  I've fixed it that way.

This is also included in pull request #428.

[jamespetts]

Splendid, thank you: now incorporated.