ImageCache keyed by const char* hashes/compares the pointer. not the content

[kimkulling]

Describe the bug
ImageCache keyed by const char* (tinyui.h:160): hashes/compares the pointer, not the string — so the cache lookup at widgets.cpp:51
misbehaves across different pointers holding equal paths. Correctness-adjacent, but it also defeats the cache (duplicate loads).
Use std::string as the key.

To Reproduce

1. Add an image to the imagecache
2. Use 2 different strings with the same context and add them to the cache
3. See that there will be 2 entries instead of one

Expected behavior
There shall only one entry.

Screenshots
NA

Desktop (please complete the following information):

• OS: All