Hide xsct features if not supported by server/driver

[tari01]

fixes https://github.com/AyatanaIndicators/ayatana-indicator-display/issues/70

[sunweaver]

Took another look. I am not convinved of using bVirtualX everywhere in the code and making the appearance of the sliders depend on the bVirtualX boolean value. There could be tons of reasons to hide those sliders (e.g. desktop envs that don't support xsct such as Budgie), so a generic approach would be:

• during indicator initialization, check if we can handle brightness adjustments
• during indicator initialization, check if we can handle colortemp adjustments
• (depending on whatever reasons)
• and then later in the code, check for both feature flags individually, called by a name that describes what it is about

[sunweaver]

@tari01 Please comment on my other suggestions / requests. Thanks.

[tari01]

Took another look. I am not convinved of using bVirtualX everywhere in the code and making the appearance of the sliders depend on the bVirtualX boolean value. There could be tons of reasons to hide those sliders (e.g. desktop envs that don't support xsct such as Budgie), so a generic approach would be:

* during indicator initialization, check if we can handle brightness adjustments

* during indicator initialization, check if we can handle colortemp adjustments

* (depending on whatever reasons)

* and then later in the code, check for both feature flags individually, called by a name that describes what it is about

Since the xsct call always succeeds, the only thing we can do is check for e.g. is_budgie and all other known cases where xsct has no effect, and use something like bUnsupported. Because this pull request only fixes the virtual display issue, any further filtering should be added as another issue + fix.

[sunweaver]

Alright then.