Open the source file when the rehex-meta file is opened (allow associating the file type with the program)

[Poikilos]

Actual behavior:

• When the program opens a rehex-meta file, it opens the project file itself (such as 'something.bin.rehex-meta")--The JSON is displayed as binary.

Expected behavior:

• If the opened file is a rehex-meta file, open the corresponding binary file (such as "something.bin") if present.

Steps to reproduce issue:

1. Create a file named "something.bin" and save it using rehex to generate a "something.bin.rehex-meta" file.
2. To test on a command line, run rehex something.bin.rehex-meta then skip steps 3-4 below.
3. Associate rehex-meta file with rehex.
4. Double-click the rehex-meta file.

[solemnwarning]

Implemented in a6f3dd1