Gamemode dependent block outline rendering.

[gracien-app]

Description

This PR fixes the case where blocks are given target outlines when player's current gamemode is Spectator mode.

Block targetability is determined in function returning targeted block position. Returning nil value in aforementioned function naturally prevents rendering of block outline in worldRenderer main render loop (no block position data available).

Initial approach was to use computed variable in worldRender, however, proposed solution seemed much more elegant (single thread-safe player data fetch).

Fixes #137

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation comments
• [x] My changes generate no new warnings

[stackotter]

I'll just wait for the build action to finish before merging just in case