This deprecates the (internal) use of package URLs and instead replaces with `datasource`/`lookupName`.

Closes #3005 

Closes #1764 

Renames currentVersion to currentValue, newVersion to newValue, newVersionMajor to newMajor, and newVersionMinor to newMinor.

This PR replaces the existing `pinVersions`, `upgradeInRange` and `versionStrategy` settings with a single one: `rangeStrategy`.

Previously:
 - `pinVersions` could be `true` or `false`, but defaulted to `null`, which meant that Renovate would decide. `true` meant that Renovate would replace existing ranges like `^1.0.0` with an exact/pinned version such as `1.2.0`.
 - `upgradeInRange` could be true or false, default to false. If `true`, it would mean Renovate would replace an existing range like `^1.0.0` with something like `^1.2.0`
 - `versionStrategy` could be `replace` or `widen` and was mainly used for `peerDependencies` to widen existing ranges, e.g. from `^1.0.0` to `^1.0.0 || ^2.0.0`

It was possible to set conflicting settings, e.g. configuring `pinVersions=true` and `upgradeInRange=true`.

Now, we combine them into a single setting: `rangeStrategy`:
 - `auto` = Renovate decides (this will be done on a manager-by-manager basis)
 - `pin` = convert ranges to exact versions
 - `bump` = same as `upgradeInRange` previously, e.g. bump the range even if the new version satisifies the existing range
 - `replace` = Same as pinVersions === false && upgradeInRange === false, i.e. only replace the range if the new version falls outside it
 - `widen` = Same as previous versionStrategy==='widen'

Rewrite of dependency extraction, particularly for npm. Paves way for easier addition of new package managers.

Closes #1882