clean up the boot process

[cash]

Here are the issues:

1. library loading has two for loops when only one is needed

2. library loading should be order independent (rather than requiring actions.php and database.php to be loaded first)

3. there is a mix of functions being called directly from start.php and functions registered for the 'boot', 'system' event

4. there is code in start.php that can be moved into functions

5. there is confusion between loading configuration for Elgg as an application (think datalists stuff) and as a site (think config table or ElggSite entity).

I was trying to working on caching and the way the code was distributed made it difficult to understand/change.

My attempt at cleaning this up: ​https://github.com/cash/Elgg/tree/boot

[Cash Costello]

Merge pull request #150 from cash/boot

Fixes #4317 cleans up the boot process

Changeset: 54bef9fc0b85acaf6950e618bd02aa50befd2acc

[Cash Costello]

Merge pull request #150 from cash/boot

Fixes #4317 cleans up the boot process

Changeset: 54bef9fc0b85acaf6950e618bd02aa50befd2acc