PediaIcons Parser - Be Able to Read in Tech Icons

[QuintillusCFC]

Add the ability to read the PediaIcons.txt file, at least enough to parse out pedia icons for techs.

These will be used in the tech selection dialog.

Reference for this being done in Quintillus's editor: https://hg.sr.ht/~adj/civ3_shared_components/browse/src/main/java/com/civfanatics/civ3/pediaIcons/PediaIconsFile.java?rev=tip

Note that a more robust solution may be pursued, and that implementation doesn't (as of Feb. 8, 2023) handle forward slashes on Linux/Mac.

These should be stored on the technology objects.

[WildWeazel]

I had started on some code related to this- check with me before working

[TomWerner]

This was done in #516.